Optical pulse chopper

ABSTRACT

A method of producing narrow optical pulses includes receiving first and second optical pulses having first and second widths, respectively, the second optical pulse having a delay relative to the first optical pulse, and selectively interfering the first and second optical pulses to produce a third optical pulse having a third width narrower than both said first and second widths.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a National Phase Application of PCT InternationalApplication No. PCT/US02/09969, International Filing Date March 28,2002, which is a continuation-in-part application of U.S. applicationSer. No. 09/819,589 filed Mar. 28, 2001, now U.S. Pat. No. 6,603,904,and claims the benefit US Provisional Patent Application, 60/356,089,filed Feb. 11, 2002.

FIELD OF THE INVENTION

The invention relates to optical communications and more particularly tothe modulation and switching of data on optical channels using physicaleffects involving the combination of energy in light beams in variousways.

BACKGROUND

In the field of optical communication, there is a pressing need toimprove the capacity of optical networks and the speed of switching atreasonable cost. These are attended by the related problems of efficientretrofit to existing infrastructure, ease of maintenance, reliability,etc. The physical media of optical fibers used in current generationoptical networks have a tremendous as yet untapped reserve capacity. Thereasons for this involve various bottlenecks, chief among them, the slowspeed of switches for optical data. To switch optical data, either thedata on an optically-modulated signal must be converted to electricalmodulation and switched by electrical switches or slow mechanicalswitches must be used. Even the latter involves the slow conversion ofoptical modulation into electrical signals for control of the mechanicalswitches. To compensate for the slowness of the conversion and switchingprocesses, substantial parallelism must be introduced into the design ofswitches resulting in high cost. In either case, currently, there is noanalog to the network switches used in electrical networks, whereswitching introduces minimal delay in the propagation of networksignals.

In addition to the switching process per se, the process of generatingoptical signals—the modulation itself—is slow because of the rise andfall times of current optical modulators. As a result, symbols are muchlonger than need be, thereby limiting the bandwidth to a levelsubstantially below the potential of the optical media.

A technique called Wavelength Division Multiplexing (WDM) and arefinement called, Dense Wavelength Division Multiplexing (DWDM) arecurrently used to increase the capacity of optical media using currentmodulation technology. WDM or DWDM methods increase the transmissionrate by creating parallel information channels, each channel beingdefined by a different light frequency. Another method, Time DivisionMultiplexing (TDM) exists in which multiple data sequences areinterleaved in time-division fashion on a common medium.

WDM or DWDM methods increase the transmission rate by using parallelinformation channels. The information in each optical channel is carriedby a different light frequency. The light frequencies of the channelsare combined together and are inserted into the input of a singleoptical fiber. The combined light frequencies at the output of the fiberare separated into different parallel channels, one for each specificlight frequency. Although DWM and DWDM has the ability increase thecapacity of a fiber, the number of channels that may be defined has apractical upper limit because of the limited bandwidth of the fiber(optical properties are attuned to a narrow range of frequencies) andbecause of the ability of the laser sources to contain their energy invery narrow frequency bands.

In TDM, the bits of several parallel channels at the same lightfrequency are interleaved in a predetermined periodic order to create asingle serial data stream. This method is very effective when using abuffer, which accumulates and compresses the data of several channelsinto a dense serial data stream of a single channel by reorganizing thisdata with suitable delays. However the data rate permitted by thismethod as well as others is still limited by the data rate and dutycycle of the light sources (DFB and DBR lasers) themselves. That is, indirect modulation, the power to the laser is switched on and off. Therate at which this can occur has a physical upper limit due to therelatively long recovery time of the lasers and it produces chromaticdispersions due to broadening of the emitted spectral line of themodulated lasers. This is caused by spontaneous emission, jittering, andshifting of the gain curve of the lasers during the current injection.Where modulation is performed in an indirect manner, the lasers areoperated in a Continuous Wave (CW) mode and separate modulators performthe modulation of the beam. The modulators are usually made frominterference devices such as Mach-Zender's, directional couplers andactive half wave-plates combined with polarizers and analyzers. However,an electro-optical must be activated to modulate the beam; to producephase shifts and polarization changes. Such changes involve the creationand removal of space charges, which change the density of the chargecarriers within these electro-optic materials. The formation rate of thespace charges is mainly dependent upon the speed and the magnitude ofthe applied voltage and can be on the order of sub nanoseconds. Thecharge removal is usually slower and is mainly dependent upon therelaxation time of these materials (lifetime of charge carriers) and canbe relatively long. Accordingly, the width of the pulses and the dutycycle of the modulation are dependent limited by the long off-time ofthe modulators.

These same rise and fall time limitations impose similar limits on theabilities of switches to direct light along alternative pathwaysaccording to routing commands and data. At present, there are two majorclasses of optical switches. In one class, optical signals are convertedto electrical signals, routed conventionally, and optical signalsgenerated anew at the output. As discussed above, the process ofconversion is slow and involves many parallel channels making suchswitches costly as well. This class of switches goes by the identifierOEO, which stands for optical-electrical-optical. A second class ofswitches goes by the identifier OO, which stands for optical-optical. Inthese switches, no conversion of optical signals to electrical signalstakes place. Instead, the optical energy is routed by means of some sortof light diversion process such as a switchable mirror. In one system,micromechanical actuators or so-called MEMS motors are used to movemirrors in response to electrical routing signals. The speed of suchswitches is again limited by the need to process electrical signals andthe slow response of energy conversion in the MEMS motors. The result isa need for multiple channels to be provided and great expense as well asdelay in the speed of the signals along the selectable data routes.

At present, the highest bit rate that can be achieved is about 10 G bitsper channel, which is limited by the modulation rate of the modulators,the pulse width that they produce, and the switching time of theelectronic switches.

As a result of the foregoing limitations of the prior art, there is aneed for reliable mechanisms for exploiting the physical potential offiber optic media in terms of data rate, switching, and cost.

SUMMARY OF THE INVENTION

An all-optical system for modulating, switching, multiplexing,demultiplexing, and routing optical data employs control units thatdirect light energy according to a coincident control signal which isalso in the form of light. In an embodiment, a control unit directs asubstantial fraction of the energy (and included symbols) in a datasignal to a first output when a light control signal is simultaneouslypresent at a control input of the control unit and to a second outputwhen the light signal to the control input is absent. That is, when thecontrol signal and the data signal are coincident at the respectiveinputs of the control unit, most of the data signal energy is directedto one output and when the control signal is noncoincident with the datasignal, most of the data signal energy is directed to another output.According to an embodiment, this “coincidence-gate” behavior is broughtabout by the interference of the control and data signals. Note that thecalling one signal a control signal and the other signal a data signalis, at least in many embodiments, purely an arbitrary choice and is usedin the present specification heuristically to facilitate the descriptionof the invention.

In an embodiment, the interference of light in the control and datasignals is the result of applying one signal to a first diffractiongrating that generates a first interference order diffraction patternand the other signal to a diffraction pattern adjacent or interleavedwith the first such that a different interference order is generatedwhen both signals coincide on both gratings. In an example, the firstgrating may be a transmission grating with (broken) reflective surfacesbetween the transmission apertures defining a reflection grating. Withsuch a device, one signal may reflect off of the reflective grating andthe other signal may pass through the transmission grating. Thereflection and transmission diffraction patterns of either signalproduces first order diffracted radiation when only one signal falls onthe device at given instant of time. But when both fall on the device atthe same time, so that the effective pitch of the diffraction gratingincludes both the transmission and reflection grating, a lower orderdiffracted radiation results. In the case of the first order pattern,the lobes have different directions and/or intensities from that of thelower order diffraction pattern. With suitably spatially-locatedreceivers, the energy may be directed in different directions from thistype of interference device depending on whether the two signals arecoincident or noncoincident. The coincidence gate may thus have acoincidence output to which energy is sent when the both inputs receiveenergy at the same time and a noncoincidence output to which energy issent when the inputs receive energy at different times. Note, as shouldbe clear to a person of ordinary skill, for the above interference typeof coincidence gate to work properly, the phases of the inputs should beproperly aligned to insure the energy from the gratings falls on therespective receivers.

Preferably the first and lower order diffraction patterns are first andzero order diffraction patterns to minimize the number of energypickups. That is, the effective number of lobes increases with the ratioof the pitch to the wavelength. This makes it necessary to provide morepickups to collect most of the energy in the lobes as the orderincreases. To achieve this in the case of a grating, the wavelength ofthe light should be in appropriate ratios to the pitches of thetransmission/reflection and combined gratings, as may be determined byrelationships well-known in the art. Generally, this will be achieved bychoosing a low order grating.

Using such an interference device as described above, by suitableconstruction of an optical device, incident energy is directed alongdifferent paths depending on whether the data and control beams arecoincident on the inputs to the interference device or noncoincident.The result is a basic component, mentioned above, called the coincidencegate. This gate may be used to control the path of a data signal. Forexample, by articulating a single data signal so that it contains pairsof pulses separated by a predefined spacing, and splitting this signal,sending one to one input of the coincidence gate and sending a delayedversion to the other input of the coincidence gate, the signal will betransmit a pulse at one output of the coincidence gate when the pulsespacing matches the delay and through another output when the pulsespacing is different from the delay. By sending such a pulse to a numberof different coincidence gates, each with a different delay, thearticulated signal will only produce a pulse at a selected output in thegate provided with the delay matching the spacing of the pulses in thesignal. Thus, the optical signal carries a symbol (the pulse spacing)that selects which coincidence gate-device its energy will be sentthrough. This effect amounts to a basic switching function. Note thatthe switching function can be layered by providing each output toanother set of different gates each with another different delay. Toarticulate the signal for successive layers, each pulse pair must bedefined by a pulse pair. This signal construction must be repeated, infractal-fashion, for every switch layer involved because each pulse paironly produces a single pulse at the output. The details of this processare described in the Detailed Description section along with supportingillustrations.

The coincidence device may also be used to create a modulator for signaltransmission because of its rapid on-off response. That is, if two broadpulses are applied to the control and data inputs of a coincidencedevice with different time delays, the width of the pulse emerging fromthe coincidence output will be determined by the period during whichboth input pulses fall on the grating at the same time.

The coincidence effect can be used to generate pulses that are verynarrow. By combining multiple ones of such pulse-shaving devices feedinginto a common optical channel, very dense streams of narrow pulses maybe generated thereby increasing the bandwidth of an optical signal. Amirror-image process can then be used to generate data streams withlarger pulse spacing along multiple channels at a receiver. Thus, theabove description embodies a multiplexer/demultiplexer combination.

The above-described diffraction grating device is only one of a numberof alternative interference devices that may be used to create acoincidence device. A very similar type of device formed from waveguidesmay be used to produce diffraction patterns from control and data inputswith spatially-separated receivers. In addition, Y-junctions,directional couplers, fast-pitch diffraction gratings, beam splitters,for example, may be used as the bases of non-diffraction interferencedevices to produce a similar coincidence function. Examples of suchdevices are described in the Detailed Description section below alongwith supporting illustrations.

Also, in addition to the modulation and self-switching functionsdescribed above, the coincidence gate may be used as the basis for aswitch controlled by an external control signal. Thus, a data signalfrom one source can be directed to an appropriate output of a layer ofcoincidence gates by sending an appropriately-timed control pulse to allof the gates. Alternatively, a single selected coincidence gate can haveone of its outputs selected by an external control signal bytransmitting a control signal to only the selected coincidence gate.

An additional layer of symbology may be added to an optical signal whichmay be used for switching purposes in coincidence gates employing thediffraction phenomenon. The propagation directions of the variousdiffraction orders may be varied by imposing different phaserelationships between the data and control signals. By placing receiversin different locations, each set with different outputs, the coincidencegate may be configured to provide selectable outputs depending on thephase relationship between the pulses.

The invention will be described in connection with certain preferredembodiments, with reference to the following illustrative figures sothat it may be more fully understood. With reference to the figures, itis stressed that the particulars shown are by way of example and forpurposes of illustrative discussion of the preferred embodiments of thepresent invention only, and are presented in the cause of providing whatis believed to be the most useful and readily understood description ofthe principles and conceptual aspects of the invention. In this regard,no attempt is made to show structural details of the invention in moredetail than is necessary for a fundamental understanding of theinvention, the description taken with the drawings making apparent tothose skilled in the art how the several forms of the invention may beembodied in practice.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 a and 1 b are illustrations of certain principles of opticsinvolved in the operation of a diffraction grating-based embodiment ofthe inventions disclosed.

FIGS. 2 a and 2 b are illustrations of certain principles of opticsinvolved in the operation of transmitting and reflecting gratingscombined together, in accordance with an embodiment of the inventionsdisclosed.

FIG. 3 illustrates an interference pattern of a combined gratingutilized in certain embodiments of the inventions disclosed.

FIG. 4 is an illustration of an interference pattern of a combinedgrating irradiated from two directions for purposes of explainingcertain embodiments of the inventions disclosed.

FIG. 5 shows interference patterns of the combined grating withdifferent illuminations for purposes of describing certain principles ofoptics involved in the operation of certain embodiments of theinventions disclosed.

FIG. 6 a illustrates the controlling of the interference patterns of acombined grating for purposes of explaining certain principles of opticsinvolved in the operation of embodiment of inventions disclosed.

FIG. 6 b is an illustration of all-optical switching of an informationcarrier-beam between ports using a control beam according to certainembodiments of inventions disclosed.

FIG. 7 a shows additional all-optical design for controlling theinterference patterns of a combined grating employed in certainembodiments of inventions disclosed.

FIG. 7 b is an illustration of an additional design for all-opticalswitching of an information carrier-beam between ports using a controlbeam according to certain embodiments of inventions disclosed.

FIG. 7 c are graphs showing all-optical switching of an informationcarrier-beam between the ports using different pulse width and timedelays between the carrier and control beams according to certainembodiments of inventions disclosed.

FIG. 8 a shows another all-optical design for controlling theinterference patterns of a combined grating according to certainembodiments of inventions disclosed.

FIG. 8 b illustrates additional an all-optical switching device forswitching the information carrier beam between ports using the controlbeam according to certain embodiments of inventions disclosed.

FIG. 9 is an illustration of various alternative design features for acombination transmitting and reflecting grating according to certainembodiments of inventions disclosed.

FIG. 10 a shows another variation on an optical switching componentproviding greater energy transfer and/or ports according to certainembodiments of inventions disclosed.

FIG. 10 b is an illustration of a retrofit embodiment for a switchcomponent according to certain embodiments of inventions disclosed.

FIG. 11 a shows an all-optical switching and modulating system using aninterference optical waveguide device according to certain embodimentsof inventions disclosed.

FIG. 11 b illustrates an all-optical switching and modulating systemusing an interference device made of optical waveguides and output portsaccording to certain embodiments of inventions disclosed.

FIG. 11 c is an illustration of an all-optical switching and modulatingsystem with a self-control feature according to certain embodiments ofinventions disclosed.

FIG. 11 d illustrates a different design for an all-optical switchingand modulating system with control symbology integrated in aninformation beam according to certain embodiments of inventionsdisclosed.

FIG. 12 shows all-optical switch that is self controlled using apredetermined code.

FIG. 13 illustrates a symbology usable with an all opticalencoding/decoding system of embodiments of the inventions.

FIG. 14 illustrates a demultiplexer usable with optical an all opticalencoding/decoding system of embodiments of the inventions.

FIGS. 15 a and 15 b illustrate an ultra-fast all-opticalmodulator/switch and an all-optical multiplexing device made therefrom,respectively, according to embodiments of inventions disclosed.

FIG. 15 c shows an all-optical network system including an all opticalsystem for multiplexing and demultiplexing connected by a long-haulfiber optic channel according to embodiments of inventions disclosed.

FIG. 16A illustrates a mechanism for taking long pulses typicallygenerated by current technology and chopping them to make very narrowpulses using mechanisms in accord with embodiments of the inventionsdisclosed.

FIG. 16B illustrates a mechanism for encoding a sequence of twosuccessive pulse-symbols to provide a first layer of routing informationso that they can be routed by a switch in accord with embodiments of theinventions disclosed.

FIG. 16C illustrates a mechanism for encoding a sequence of twosuccessive pulse-symbols to provide a second layer of routinginformation so that they can be routed by a switch in accord withembodiments of the inventions disclosed.

FIG. 16D illustrates a mechanism for encoding a sequence of twosuccessive pulse-symbols to provide a third layer of routing informationso that they can be routed by a switch in accord with embodiments of theinventions disclosed.

FIG. 16E is an annotated diagram illustrating an encoding scheme formultilayer switching according to embodiments of inventions disclosed.

FIG. 16F illustrates the effect of each switch layer on symbology forrouting a data pulse.

FIG. 17 illustrates a system in which a combination of WDM and a form ofsymbology provided by an invention disclosed, in which the symbology isused for CDM.

FIG. 18 shows some principles involved with directional couplers usedfor a coincidence devices according to embodiments of inventionsdisclosed.

FIG. 19 shows some principles involved with Y-couplers used for acoincidence devices according to embodiments of inventions disclosed.

FIGS. 20 and 21 illustrate basic operation of a component of acoincidence device based on direction couplers according to embodimentsof inventions disclosed.

FIGS. 22, 23, and 24 illustrate the basic operation of a coincidencegate device in first and second noncoincidence states and a coincidencestate, respectively according to embodiments of inventions disclosed.

FIG. 25 illustrates a coincidence gate device that is a variation of theembodiments of FIGS. 22–24 employing a star coupler instead of multipleY-junctions for discussing alternative design concepts.

FIG. 26 illustrates a coincidence gate device that is a variation of theembodiments of FIGS. 22–24 compatible with waveguide implementation fordiscussing alternative design concepts and for illustrating analternative way of splitting the signals at the input end of aself-triggering-type coincidence gate.

FIG. 27 illustrates a coincidence gate device that is a variation of theembodiments of FIGS. 22–24 compatible with waveguide implementation andusing a start splitter instead of directional couplers for discussingalternative design concepts.

FIG. 28 illustrates principles involved with dielectric beam splittersfor purposes of discussing alternative embodiments of inventionsdisclosed.

FIG. 29 illustrates principles involved with metallic beam splitters forpurposes of discussing alternative embodiments of inventions disclosed.

FIG. 30 illustrates energy routing in a transmission/reflection gratingof certain embodiments of inventions disclosed.

FIGS. 31 and 32 illustrate energy routing in two types of Y-junctionused in certain embodiments of inventions disclosed.

FIG. 33 illustrates energy routing in a grating with a pitch that ismuch greater than the wavelength of a light signal and which functionsin a manner that is similar to a beam splitter as used in certainembodiments of inventions disclosed.

FIGS. 34, 35, and 36 illustrate an embodiment of a coincidence devicesconsistent with certain embodiments of inventions disclosed andemploying a beam splitter and Y-junction for discussing certain conceptsof these embodiments.

FIGS. 37, 38, and 39 illustrate an embodiment of a coincidence devicesconsistent with certain embodiments of inventions disclosed andemploying a beam splitter and a different kind of Y-junction fordiscussing certain concepts of these embodiments.

FIGS. 40, 41, and 42 illustrate embodiments based on beam splitter andbeam-splitter-like coincidence devices for purposes of discussingvarious embodiments of inventions disclosed.

FIG. 43 illustrates a conceptual description of a coincidence device forabstracting certain concepts involved in various embodiments ofcoincidence devices of inventions disclosed in which the interferenceinvolves a first ratio of routed energy in the coincidence andnoncoincidence states.

FIG. 44 illustrates a conceptual description of a coincidence device forabstracting certain concepts involved in various embodiments ofcoincidence devices of inventions disclosed in which the interferenceinvolves a second ratio of routed energy in the coincidence andnoncoincidence states.

FIG. 45 illustrates a conceptual description of a coincidence device forabstracting certain concepts involved in various embodiments ofcoincidence gates of inventions disclosed.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS. 1 a and 1 b illustrate the optical operational principle of knowntransmitting and reflecting gratings, respectively. FIGS. 1 a and 1 bmay assist in understanding the present invention. FIG. 1 a shows atransmitting grating 2 with openings 4 with pitch d. Grating 2 receivesplanar radiation waves 6 on its side 8. Only part of the radiation ofthe impinging waves 6 is transmitted, by openings 4, to the other side10 of grating 2. Beam 12 exits from openings 4 and has a cylindricalwavefront (diffraction effect) and its intensity is distributedisotropically over half cylinders 14 along which it propagates.

The radiation of propagating fronts 14 (in the shape of cylinders)interfere with each other to create constructive and destructiveinterference. Arrows 16 schematically illustrate the directions alongwhich the constructive interference exist. The directions of arrows 16are indicated by angles θ, measured in radians, with respect to the axisof symmetry 18 of grating 2. Arrows 16 actually indicate the antinodesalong which beam 6 is concentrated, due to grating 2, and thus point tothe values of intensity peaks at the various angles θ, on the coordinaterelative to the normal 18. The latter is a part of plot 20, whichillustrates the spatial distribution of the radiation intensity I ofbeam 6 versus angle θ. Arrows 16 point to the angle values θ in whichthe intensity I of beam 6 reaches local maxima 22.

The mathematical relationships between intensity I of beam 6,transmitted by grating 2, and propagation angle θ of this radiation aregiven by equation (1):I∝[sin(n·β·d·sin(θ)/2)/sin(β·d·sin(θ)/2)]2  Eq. (1)

In this equation n is the number of openings 4 and β is the wave vectorof beam 6 that is equal to 2·π/λ and λ is the wavelength of beam 6.

The intensity I according to Eq. (1) reaches a local maximum value when:(β·d·sin(θ)/2))=i·π  Eq. (2)

This occurs when I is an integral number, known as the order of thediffraction.

When substituting β for 2·π/λ in Eq. (2), it takes the form:sin(θ)=i·λ/d  Eq. (3)

FIG. 1 b shows transmitting grating 32 with mask stripes 34 arrangedwith pitch d. Grating 32 receives radiation planar waves 36 on its side38. Only part of the radiation of waves 36 is reflected back by maskstripes 34 and out from grating 32. Stripes 34 have diffusive reflectingsurfaces and are very narrow (diffraction effect). Thus they reflect theradiation with equal intensity in any direction. Beam 42 reflected fromstripes 34 have a cylindrical wavefront and its intensity is distributedisotropically over half cylinders 44, defined by the locus of directionsof propagation. The beams from propagating cylinders 44 interfere witheach other to create constructive and destructive interference. Arrows46 schematically illustrate the directions along which there isconstructive interference. The directions of arrows 46 are indicated byangles θ, measured in radians, with respect to the normal 48 of grating32 surface. Arrows 46 actually indicate the orientations along whichbeam 36 is concentrated by grating 32. The values of angles θ areindicated on the θ axis. This axis is a part of graph 50, whichillustrates the spatial distribution of the radiation intensity I ofbeam 36 versus angle θ. Accordingly it is clear that arrows 46 point outthe angle values θ at which the intensity I of beam 36 reaches localmaximum values 52.

The mathematical relationships between intensity I of beam 36, reflectedby grating 32, and propagation angle θ of this radiation are given byequation (4) below:I∝[sin(n·β·d·sin(θ)/2)/sin(β·d·sin(θ)/2)]2  Eq. (4)

In this equation n is the number of stripes 34, d is the spacing betweenlines 34 and β is the wave vector of beam 36 that is equal to 2·π/λ andλ is the wavelength of beam 36.

The intensity I according to Eq. (4) reaches a maximum value when:(β·d·sin(θ)/2))=i·π  Eq. (5)

This occurs when I is an integral number known as the order of thereflection.

When substituting 2·π/λ for β in Eq. (5) it takes the form:sin(θ)=i·λ/d  Eq. (6)

For both types of the gratings, the diffraction (transmitting—FIG. 1 a)grating and the reflecting grating (FIG. 1 b), the mathematical formulasare the same.

The angles θi in which the intensity of the radiation that comes fromthe gratings is maximal are known as the diffraction orders i of thegratings. Accordingly, the angles θi of the transmission and reflectingorders are given by Eq. (7).sin(θi)=i·λ/d  Eq. (7)

This occurs when i is an integral number and can get the values +/−0, 1,2, . . . .

The incident angle φ of the incoming radiation is measured relative to anormal to the grating. When the incident angle φ, of the radiation thathits diffracting and reflecting gratings is off the normal to thegrating, i.e., it differs from an incident angle equal to zero, then Eq.(7) becomes:sin(θi)+sin(φ)=i·λ/d  Eq. (8)

This means that the whole pattern of interference is rotated by an angleφ. For a diffracting grating it means that the zero order of the gratingis located on a line along which the incident radiation propagatestoward the grating. For a reflecting grating it means that the zeroorder of the grating is located on a line that is symmetric with respectto the normal of the grating. I.e., it forms an angle that is equal inmagnitude on the opposite side of the normal of the grating surface.

FIG. 2 a is a side view and schematic illustration according to acombination 100 of transmitting and reflecting gratings formed on acommon surface 102 of transparent block 104 according to embodiments ofinventions disclosed. Block 104 can be made, for example, ofsemiconductors such as Si, GaAr, InGaAr, quartz, glass, silica, fusedsilica or plastic. A block is not essential as may be observed byinspection, but provides a convenient mechanism for manufacture andsupport of the grating. Alternatively a clear planar piece of materialmay be used to support the gratings.

Combined grating 100 includes two layers of gratings 106 and 108.Grating layer 106, on surface 102, is made of high-absorption materialthat is not transparent and has a surface with a very low reflection.For example, grating layer 106 can be made of silver oxide, which iswidely used in the field of projection masks for photolithography.

Grating layer 108 is made of a material having a surface with a veryhigh-reflectivity. For example, grating layer 108 can be made of indiumoxide in a similar way to that used to fabricate reflectors and mirrors.

Grating layers 106 and 108 can be produced by standard techniques usedto produce gratings. For example layer 106 is formed continuously oversurface 102 and coated by a photoresist material. The photoresist isexposed with Ultra Violet (UV) radiation by known holographictechniques. (Holography involves the interference of two beams having apredetermined angle between them which produce an interference pattern.)Also exposure can be made through a projection mask.

The photoresist is backed in an oven after its exposure and is dipped(or soaked) in a developer to create openings in the photoresist, abovelayer 106, in the areas that were exposed. Dipping (or soaking) thephotoresist is done in a selective etching acid, such as acetic acid,which does not attack the photo resist and surface 102. This creates, byselective etching, openings 110 in layer 106 through the openings in thephotoresist. After removing the photoresist with acetone, layer 106 onsurface 102 of block 104 takes the form of grating layer 106 havingmultiple lines 114 and multiple openings 110.

For example, the following process, known as lift-off, can producegrating layer 108:

1. Cover grating layer 106 with a layer of photoresist.

2. Create centered openings in the photoresist above lines 114 ofgrating 106, by the exposing and developing techniques described above.

3. Deposit or evaporate a continuous layer 108 on top of the patternedphotoresist.

Dip layer 108 in acetone vibrated at an ultrasonic frequency (lift-offtechnique)

The liftoff technique removes all the areas that were on top of thephotoresist material and leaves only lines 116 of reflectinggrating-layer 108; these are centered on lines 114 of grating layer 106.

The formation of grating layer 108 centered on top of grating layer 106completes the fabrication of combined grating 100.

Lines 118, 120, and 122 of block 104 have cuts 124, 126, and 128,respectively. Cuts 124, 126, and 128 indicate that the drawing of FIG. 2a is not scaled. Especially, the dimensions of combined grid 100 are notscaled. In reality the dimensions of combined grating 100 are very smallrelative to the dimensions of block 104 and they are enlarged in FIG. 2a for clarity.

For example, the widths S1, S2, and S3 of openings 110, lines 114, andlines 116 of grating layers 106 and 108, respectively, are of the sameorder of magnitude as the wavelength λ of the radiation used in opticalcommunications (about 1.3 μm and 1.5 μm). The total thickness W ofgrating layers 106 and 108 together can be less than 0.1 μm and isnegligible with respect to the radiation wavelength λ.

When planar-wave beam 132 is directed toward combined grating 100, partof it passes through openings 110 and is diffracted isotropically with acylindrical wavefront 133 to create an interference pattern based upongrating layer 106. The other part of beam 132 is absorbed by lines 114and is lost.

When planar-wave beam 134 is directed toward combined grating 100, partof it passes through openings 110 and is lost. Lines 116 of gratinglayer 108 reflect the other part of beam 134.

Reflecting lines 116 of grating layer 108 may be deposited or evaporatedat a high-rate to create a grainy surface, which produces adiffuse-reflecting surface. The diffuse-reflecting surface of lines 116reflects beam 134 isotropically as beam 136 having a cylindricalwavefront to create an interference pattern based upon grating layer108.

When planar-waves 132 and 134 are applied simultaneously, combinedgrating 100 acts simultaneously as the combination of grating layers 106and 108. When the beam to be transmitted 132 is in phase with the beamto be reflected 134 and both have equal intensities, the interferencepattern of combined grating 100 is like gratings 106 or 108. However inthis case grating 100 has half the pitch (double periodicity or doublethe density in terms of numbers of lines per unit length).

Accordingly, when only beam 132 or 134 is directed toward combinedgrating 100, then the grating 100 produces an interference pattern thatis about the same for both situations corresponding to the interferencepattern of gratings 106 or 108, respectively. When both beams 132 and134 are directed toward combined grating 100, then grating 100 producesan interference pattern that is a combination of the interferencepatterns corresponding to the interference pattern of gratings 106 and108. It is equivalent to an interference pattern of a grating havinghalf of the pitch of gratings 106 or 108. The latter is of lower orderthan either of the former patterns.

One important condition that is preferably maintained is thephase-matching between beam 133 diffracted from openings 110 of gratinglayer 106 and beam 136 reflected from lines 116 of grating layer 108.This phase-matching preferably should be maintained over and alongsurface 102. Assuming that beams 132 and 134 have the same wavelength λ,then the phase-matching depends on angles φ0, φ1, and φ2. Angles φ0 andφ1 are the impinging incident angles of beams 132 and 134 on combinedgrating 100, respectively, and are measured relative to line 138 that isnormal to grating 100 and surface 102. Angle φ2 is the angle betweenline 140 (parallel to line 122) and surface 102 when line 140 is normalto the direction in which beam 134 propagates.

Phase-matching along surface 102 is achieved when the followingmathematical condition is fulfilled:β1·sin(φ1)=β0 sin(φ0)  Eq. (9)

Here β1=2π·N1/λ and β0=β1=2π·N0/λ and N1 is the refractive-index of thematerial of block 104. N0 is the refractive-index of the air and isequal to 1. When substituting the expression for β in Eq. (9) andreorganizing its form, Eq. (9) takes the form of the optical law knownas Snell's law:N1·sin(φ1)=N0·sin(φ0)  Eq. (10)

The mathematical relationships between φ0, φ1, and φ2 are:φ0=90°−φ2andφ0=φ2  Eq. (11)

By substituting Eq. (11) in Eq. (10) and reorganizing Eq. (10) we get:φ2=arc tang(N1/N0)=arc tang(N1).  Eq. (12)

For example, if N1=1.5 then φ2=56.3°.

FIG. 2 b shows an additional design for a combined transmitting andreflecting grating designed according to embodiments of inventionsdisclosed. This design is similar to that of FIG. 2 a and thus the samenumerals are used to indicate similar parts. The design of combinedgrating 100 is achieved by bonding block 105 to block 104 of FIG. 2 a.Thus, the parts of the design in FIG. 2 b that are similar to those ofFIG. 2 a are not explained again here.

Block 105 may be made of the same material as block 104 and thus mayhave the same index of refraction. Block 105 may be bonded to block 104by index-matching glue having the same refractive index as the blocks.Such glue is commonly used in optical components. Such glue does notcause any reflection of the radiation that passes between blocks. Theabsence of such reflection hides surface 102; therefore it isillustrated by a broken line. Avoiding reflection between blocks allowscomplete transmission of beam 132 through openings 110. Because of this,the refractive index on both sides of combined grating 100 is the sameand is equal to N1.

By substituting index N0 with index N1 in Eqs. (11) &(12) we get:φ0=φ1=φ2=45°.

FIG. 3 schematically illustrates the interference pattern of combinedgrating 100. Grating 100 is illustrated according to its version shownin FIG. 2 a but it can be designed without any limitation according tothe design shown in FIG. 2 b. Beam 132 enters to transparent block 104without direction change and impinges on combined grating 100 atincident angle φ1 relative to the normal 138 of grating 100. Angles φ0,φ1, and φ2 are adjusted according to Eqs (11) and (12), with angle φ2measured relative to line 140. Beam 132 impinges on grating 100 on theside that includes grating layer 106. Part of the radiation that passesthrough openings 110 is diffracted and interferes to produce aninterference pattern. The interference pattern has three orders in whichconstructive interference exists. These project in the directions of θ0,θ1, and θ−1 indicated by beams 152, 154, and 156, respectively, andcorrespond to the interference indices i=0, 1, and −1.

Graph 150 illustrates a curve of the intensity I of (shown in relativeunits) versus the interference angle θ (measured in radians). Theinterference orders of graph 150 are indicated by their indices (i=0, 1,and −1). The axis of graph 150, along which interference angle θ ismeasured, is scaled to mach between angles θ0, θ1, and θ−1, at whichorders 0, 1, and −1 exist on this axis, and angles θ0, θ1, and θ−1 alongwhich beams 152, 154, and 156 propagate, respectively.

According to Eq. (8) the maximum value that the index of the orders ican get is the value that satisfies the relation: sin(θi)+sin(φ1)=i·λ/d.The maximum absolute value of sin(θi) is 1. The zero order on axis θ ofgraph 150 was chosen to be at the origin. This means that for thepresentation of graph 150, sin(φ1) is chosen to be zero. Thus i·λ/dshould be less than 1 for positive values of i and more than (−1) fornegative values of i. The fact that graph 150 has only three ordersmeans, according to Eq. (8), that the index i can only have the valuesof 0 and ±1 which means that the absolute value of index is less than 2(i<2). Accordingly the pitch spacing d of grating layer 106 must satisfyd<2λ.

FIG. 4 schematically illustrates the interference pattern of combinedgrating 100 irradiated from two directions. Grating 100 is consistentwith the nomenclature and description provided with reference to FIG. 2a, but can also be designed, without any limitations, according to thedesign shown in FIG. 2 b or others. Beam 132 enters transparent block104 without direction change and impinges on combined grating 100 atincident angle φ1 relative to line 138 that is normal to grating 100.Angles φ0, φ1, and φ2 are adjusted according to Eqs (11) and (12) formaintaining phase-matching between beams 133 and 136, transmitted andreflected, respectively, by grating 100. Angles φ0, φ1, and φ2 arecalculated by taking into account the value of the refractive index N 1of the material of block 104. Angle φ2 is measured relative to line 140.

Beam 132 impinges on grating 100 on the side with grating layer 106.Part of beam 132 is absorbed by lines 114 and is lost. The other part ofbeam 132 passes through openings 110 and is diffracted out from grating100, as beam 133.

Beam 134 impinges on grating 100 on its other side that includes gratinglayer 108. Part of beam 134 passes through openings 110 and is lost. Theother part of beam 134 is reflected isotropically from lines 116 ofgrating layer 108 of combined grating 100, as beam 136.

Beams 132 and 134 impinge on grating 100 simultaneously. Lines 116 arecentered between openings 110 and thus the pitch for both grating layers106 and 108 is the same. Beam 133, diffracted out from openings 110, andbeam 136, reflected from lines 116, interferes to produce aninterference pattern. The pitch of combined grating 100 is the spacebetween lines 116 and openings 110 and thus is equal to half of thepitch of grating layer 106 or grating layer 108. The interferencepattern of grating 100 has one order (zero order) in which constructiveinterference exists in the directions of θ0 indicated by beam 152 andcorresponds to the interference index i=0.

Graph 150 illustrates a curve of the intensity I of the interferedradiation (shown in relative units) versus the interference angle θ(measured in radians). The interference order of graph 150 is indicatedby its index (i=0). The axis of graph 150 along which interference angleθ is measured is scaled to match angle θ0 at which order 0 exists onthis axis, and angle θ along which beam 152 propagates.

According to Eq. (8) the maximum value that the index of the orders ican have is the value that still maintains sin(θi)+sin(φ1)=i·λ/d. Themaximum absolute value that sin(θi) can have is 1. The zero order onaxis θ of graph 150 was chosen to be at the origin. This means that forthe presentation of graph 150, sin(φ1) is chosen to be zero. Thus i·λ/dshould be less than 1 for positives values of i and more than (−1) fornegative values of i. The fact that graph 150 has only one order means,according to Eq. (8), that index i can have only the values of 0. Thismeans that the absolute value of index i<1. Accordingly the pitchspacing d of combined grating 100 must satisfy d<λ and it is half of thepitch d of grating layers 106 or 108, as derived above from Eq. (8) asexplained in connection with FIG. 3.

The above result is in agreement with the pitch relationships betweengrating layers 106 and 108 and combined grating 100.

While grating layers 106 and 108 have pitch d between openings 110 orbetween lines 116, respectively, combined grating 100 has pitch d/2between openings 110 and lines 116. On the other hand the conditions forproducing the interference patterns of graph 150 in FIG. 3 (three ordersof interference produced by grating layer 106) and of graph 150 in FIG.4 (one interference order produced by combined grating 100) are d<2λ andd<λ, respectively. These conditions are identical to the relationshipsbetween the pitches of grating 106 (or 108) and grating 100 in whichgrating 100 has half of the pitch of grating 106 (or 108).

Beam 134 is symmetric to beam 132 with respect to grating 100 in termsof phase-matching. Grating layers 106 and 108, on both sides of grating100, have the same pitch. Accordingly, it is clear that when only beam134 impinges on grating 100, it will produce an interference patternsimilar to that shown in graph 150 of FIG. 3 created when only beam 132impinges on grating 100.

FIG. 5 illustrates two graphs 150A and 150B showing two curves of theinterference intensity I versus the interference angle. The intensity Iis shown in relative units and the angle θ is measured in radians.

Graph 150B is related to the situation illustrated by graph 150 of FIG.3, which is produced by irradiating combined grating 100 from onedirection, either by beam 132 or by beam 134. The interference patternof graph 150B has three orders 0, 1, and −1 at angles θ₀, θ₁, and θ⁻¹,respectively.

Graph 150A illustrates the situation of FIG. 4, which is produced byirradiating combined grating 100 from two directions and simultaneouslyby beams 132 and 134. The interference pattern of graph 150A has onezero order at angle θ₀.

The fact that each of the three interference orders 0, 1, and −1 appearsat different angles θ₀, θ₁, and θ⁻¹, respectively, allows the separatecollection of the radiation of each order. Accordingly orders 0, 1, and−1 of the interference pattern shown in graph 150B can be collected byonly three ports P₀, P₁, and P⁻¹, respectively.

As illustrated in FIG. 6 b (discussed in detail below) ports P₀ and P⁻¹can be joined together into one port P₂ in such a way that the beamsthey collect and transfer to port P₂ cancel each other under theconditions illustrated in graph 150B. In this configuration, illustratedin graph 150B, the output at port P₂ is zero (the difference between theintensities of order 0 and −1) and the output at port P₁ contains theintensity of order 1.

For the same configuration and for the situation illustrated in graph150A, the output, at port P₀, contains the intensity of order 0 that isthe only existing order. Order −1 has zero intensity and thus thedifference between the intensities of orders 0 and −1, which appears inport P₂, equal the intensity of order 0. In this case, the output atport P₁, which equals the intensity of order 1, is equal to zero.

Accordingly, for the configuration of ports P₀, P₁, P⁻¹, and P₂,described above, the output of port P₂ is zero for the situation shownin graph 150B. This is related to the case when grating 100 isirradiated only from one side, either by beam 132 or by beam 134. On theother hand, for the situation shown by graph 150A, which is related tothe case where combined grating 100 is irradiated simultaneously on bothof its sides by beams 132 and 134, port P₂ contains the intensity of theonly existing order, order 0.

Similarly, for the configuration of ports P₀, P₁, P⁻¹, and P₂, describedabove, the output of port P₁ contains the intensity of order 1 for thesituation shown in graph 150B. this is related to the case when combinedgrating 100 is irradiated simultaneously on both of its sides by beams132 and 134. On the other hand, for the situation shown by graph 150A,related to the case when grating 100 is irradiated only from one sideeither by beam 132 or by beam 134, port P₁ contains the intensity oforder 1, which is zero.

Thus we have moved from irradiating grating 100 simultaneously on bothof its sides by beams 132 and 134 to irradiating grating 100 only on oneof its sides by either beam 132 or beam 134. This move switches theradiation intensity from port P₂ to port P₃ and vice-versa.

FIG. 6 a—Controlling Interference Patterns of Combined Grating

FIG. 6 a illustrates optical system 200, which controls interferencepattern 150 (not shown) of combined grating 100, by controllingdifferent illuminations of beams 132 and 134 on grating 100. Opticalfiber 202 guides and emits beam 132 toward lens 204 that converts beam132 to parallel beam 132. Beam 132 is the information carrier beam usedin optical communication. Reflector 206 receives beam 132 and reflectsbeam 132 toward attenuator 208, which transmits beam 132 towardtransparent block 104. Beam 132 enters block 104 without directionchange and propagates in block 104 toward grating layer 106 of combinedgrating 100.

Laser 210 is optically coupled to optical fiber 212 and is controlled bycontrol unit 214. Fiber 212 guides and emits beam 134, produced by laser210, toward lens 216 that converts beam 134 into parallel beam 134.Beams 132 and 134 have the same wavelength λ and lenses 204 and 216 canbe, for example, of the type of Graded Index (GRIN) lens commonly usedto expand the beams emitted from optical fibers. Lens 216 directparallel beam 134 toward reflector 218 that reflect beam 134 towardgrating layer 108 of combined grating 100.

Incident angles φ1 and φ0 of parallel beams 132 and 134, respectively,and angle φ2 dictate the orientation of combined grating 100. Theseangles are adjusted to maintain phase-matching between beam 132,transmitted by grating 100 and beam 134, reflected by grating 100.Attenuator 208 is adjusted to assure that the intensity of beam 132,transmitted by grating 100, is equal to the intensity of beam 134,reflected by grating 100.

Wen control unit 210 turns off laser 210, beam 134 does not exist. Inthis case only beam 132 impinges on combined grating 100 on the sidethat includes grating layer 106. The latter has a pitch spacing d thatsatisfies, for example d<2λ. Grating layer 106 of combined grating 100acts as a diffraction grating on beam 132 and produces interferencepattern 150 of three beams corresponding to interference orders havingindices i=0, 1, and −1. In this case the interference pattern 150produced by beam 132 and grating layer 106 of grating 100 is similar tothe interference pattern illustrated by graph 150B of FIG. 5.

When control unit 214 turns on laser 210, beams 134 and 132 hit thecombined grating 100 on both of its sides, including grating layers 106and 108. Beam 132 impinges on combined grating 100 on its side thatincludes grating layer 106 and beam 134 impinges on combined grating 100on its other side that includes grating layer 108. Reflecting lines 116of grating layer 108 that reflect beam 143 are centered between openings110 of grating layer 106, which transmits beam 132. Thus grating layers106 and 108 have the same pitch d. Thus, combined grating 100 has apitch d that is half the pitch d of gratings 106 and 108. Accordingly,pitch d of combined grating 100 satisfies the relationship d<λ. Combinedgrating 100 acts on beams 132 and 134, impinging on both of its sidessimultaneously, and produces interference pattern 150 of one beamcorresponding to interference order having only the index i=0. In thiscase interference pattern 150 produced by beams 132, 134 and combinedgrating 100 is similar to the interference pattern illustrated by thecurve of graph 150A of FIG. 5.

Each time control unit 214 turns off control beam 134, interferencepattern 150 includes three beams (interference orders 0, 1 and −1). Inthe complementary cases when control unit 214 turns on control beam 134,the interference pattern 150 includes only one beam (interference orders0) and orders 1 and −1 disappear. In these cases, grating layer 106 andbeam 134 produce interference pattern 250, which has three beams(interference orders 0, 1, −1), which change their orientation accordingto Snell's law while exiting block 104. Interference pattern 250 existsevery time that beam 134 is on, even when beam 132 is off.

FIG. 6 b illustrates the optical system 200 of FIG. 6 a, describedabove, with receivers or ports P₀, P₁, P⁻¹, and output ports P₂, and P₃arranged to receive and convey energy from the interference pattern 150via a coupling lens 226. When control beam 134 is off, interferencepattern 150 includes three beams. These beams correspond to interferenceorders having the indices i=0, 1, −1 and are optically coupled bycoupling lens 226 into ports P₀, P₁, and P⁻¹, respectively.

Ports P₀, P₁, and P⁻¹ may be the inputs of optical fibers 230, 232, and234, respectively. Fiber 230, 232, and 234 guide the radiation fromtheir inputs to their outputs (ports P₂ and P₃), respectively.Accordingly fiber 234 guides the radiation of interference order −1 toits output P₃. Instead of optical fibers, the ports may be termini ofother types of optical channel mechanism such as a waveguide, lightpipe, mirrors, optical network, etc. depending on the downstreamprocesses to be used. In the current device, further processing isprovided to direct most of the energy toward a signal at port P₂ for anon-interference condition and one at port P₃ for a coincidencecondition.

Directional coupler 224, whose coupling length l is adjusted to producea 3 dB directional coupler, couples fibers 230 and 232. In coupler 224,half of the intensity in fiber 230 is transferred to fiber 232 with aphase shift of j where j is a complex number equal to (−1)^(1/2).Similarly, half of the intensity in fiber 232 is transferred to fiber230 with a phase shift of j that is equivalent to phase shift of π/2radians.

Phase shifter 220 shifts the phase of the radiation in fiber 232 by π/2radians prior to the propagation of the radiation into the couplingregion of directional coupler 224. Accordingly the radiation transferredfrom fiber 232 to fiber 230 has a phase shift of π/2+π/2=π radiansrelative to the radiation that propagates in fiber 230.

The initial radiation intensities of the beams in ports P₀ and P₁ arethe same and equal to I. The intensity of the radiation in fiber 230after directional coupler 224 is the sum of half of the initialradiation I in fiber 230 and half of the initial radiation I in fiber232, which has a relative phase difference of π radians. Thus the totalradiation intensity in fiber 230 at port P₂ is I/2−I/2=0. This meansthat when control beam 134 is off, the intensity at port P₃ is I and theintensity at port P₂ is zero.

Alternatively when control beam 134 is on, interference pattern 150includes only one beam corresponding to interference index i=0. Thelatter is coupled, by lens 226, into the input of fiber 230 through portP₀. Interference orders i=1 and −1 disappear and no radiation is coupledby lens 226, into fibers 232 and 234 through ports P₁ and P⁻¹. Thus theintensity at port P₃ is zero. Half of the radiation coupled into fiber230 at port P₀ is lost at directional coupler 224 and the remaining halfpropagates along fiber 230 to port P₂. This means that when beam 134 inon, the intensity at port P₃ is zero and the intensity at port P₂ ishalf of the initial intensity at port P₀. Accordingly, by turningcontrol beam 134 on and off, the intensity of beam 132 can be switchedfrom port P₃ to port P₂, and vice-versa.

The above description for the switching capability of the system of FIG.6 b is true for both operation modes of information carrier beam 132—theContinuous Wave (CW) mode and the pulse mode.

Phase shifter 220 can be of the type that applies pressure, by use of apiezoelectric crystal, on optical fiber 232 to change its refractiveindex and thus to change the phase of the radiation that propagates infiber 232. Phase shifter 220 can be of the type that thermally changesthe refractive index of fiber 232 to change the phase of the radiationthat propagates in this fiber.

Alternatively, shifter 220 can be made of semiconductor materialfabricated by thin film techniques that change its refractive index dueto injection of charge carriers into its guiding media. This change inthe refractive index shifts the phase of the radiation propagating inthe media of shifter 220. In this case the shifter is a separate deviceand is not an integral part of fiber 232 and thus should have two portsfor coupling fiber 232 into and from device 220. In all the above typesof phase shifter 220, applying voltage to shifter 220 through electrode222 activates shifter 220. Adjustment of the phase shift of shifter 220is achieved by adjusting the applied voltage on electrode 222.

Phase matching can be obtained by use of a suitable calibration byclosed-loop control. A calibration signal my be passed through theinputs of the devices of any of the foregoing embodiments and the phaseadjusted by means of device such as a phase shifter 220 to provide theproper phase matching. As should be clear from the foregoing discussion,when the phases of the input signals match, the p₂ output, for example,should provide a peak. Due to temperature change, the properties ofvarious optical components may drift, requiring the correction of thephase match. But this correction need only be done at fairly longintervals relative to the rate of data throughput through such devicesand therefore does not present a significant obstacle. Suitable controlsystems for performing calibration are well within the state of the artand can be embodied in many different forms. The subject is thereforenot crucial to the inventions disclosed and is therefore not discussedin greater detail herein.

FIG. 7 a schematically illustrates an optical system 300 that is similarto optical system 200 of FIG. 6 a. System 300 of FIG. 7 a differs fromsystem 200 of FIG. 6 a only in the manner of where the control beam 134comes from. Whereas in system 200 laser 210, controlled by unit 214,produces control beam 134, such control beam 134, in system 300, isproduced by coupling part of the radiation of information-carrier beam132 from optical fiber 202, into optical fiber 304. Directional-coupler302 is a 3 dB directional coupler. Thus coupler 302 couples half of theenergy of carrier beam 132 from fiber 202, in which beam 132 propagates,into fiber 304. The other half of the energy of beam 132 continuespropagating along fiber 202 and is emitted out from port P₄ at theoutput of fiber 202. The radiation energy that is coupled into opticalfiber 304 propagates and guided along this fiber through delay-fiber 306and is emitted, as control beam 134, from fiber 304 at its outputthrough port P₅. Beams 132 and 134 are converted, by lenses 204 and 216,into wide beams 132 and 134, respectively, in the same way that thisconversion is performed in system 200 of FIG. 6 a.

The rest of the optical paths of beams 132 and 134, started from lenses204 and 216 in system 300, respectively, are similar to the opticalpaths of beams 132 and 134, beginning from lenses 204 and 216 in system200, respectively, as illustrated by FIG. 6 a. The correspondingdiscussion is therefore omitted here.

Similarly, interference patterns 150 and 250 are produced, by beams 132and 134, in a similar way, in both systems, system 200 and system 300 asillustrated in FIGS. 6 a and 7 a and explained above in the explanationof FIG. 6 a. Thus the explanations given above for FIG. 6 a will not berepeated here.

Reflector 218 is arranged to move along arrows 308 to gently adjust thelength of the optical path between reflector 218 and combined grating100 to assure phase-matching between beam 132 passing through grating100 and beam 134 reflected from grating 100. While reflector 218 movesalong arrows 308 it also causes undesired shifting of the beam 134direction (indicated by arrows 310). To avoid any irradiation change ofgrating 100 by the movement of beam 134 along arrows 310, anon-reflecting, non-transmitting frame with high absorbency may beformed in the surrounding of grating 100. Frame 312 is narrower than thewidth of beam 134 and thus when bean 134 moves along arrows 310, thewhole area of grating 100 remains irradiated.

Delay-fiber 306 produces a time delay Δt between control beam 134 andcarrier beam 132. An explanation of how the amount of delay Δt affectsinterference patterns 150 and 250 is given below in the explanations forFIG. 7 c.

FIG. 7 b illustrates the same optical system 300 of FIG. 7 a, describedabove, with additional ports P₀, P₁, P⁻¹, P₂, and P₃ arranged to receiveinterference pattern 150 from coupling lens 226. Switching the emissionof the radiation of information carrier-beam 132 between ports P₂ and P₃of optical fibers 230 and 234 is achieved by changing interferencepattern 150, having three beams (three interference orders i=0, 1, and−1) to only one beam (interference order i=0). The interference pattern150 dictates which of ports, P₂ or P₃, is the one that emits carrierbeam 132 in accord with the description attending FIG. 6 b providedabove.

Delay-fiber 306 produces a time delay Δt between what might be termed acontrol beam 134 and data beam 132. The amount of delay Δt affectsinterference patterns 150 and 250 and thus dictates the switching statebetween port P₂ and P₃. An explanation of how the amount of delay Δtaffects interference patterns 150 and 250 and thus the switchingposition between ports P₂ and P₃ is given below in the explanations forFIG. 7 c.

FIG. 7 c shows graphs 356, 358, 360, and 362 of the radiation intensityI versus time t for information-carrier beam 132, control beam 134, theradiation emitted from port P₂, and the radiation emitted from port P₃,respectively. P₂ and P₃ are the ports illustrated by FIGS. 6 b and 7 band all the pulses in the above graphs have width T. Intensity I ingraphs 356–362 is shown in arbitrary units and there is no proportionbetween the intensity I of different graphs 356–362.

Graphs 356–362 are gathered in several groups classified according tothe time delay Δt between information carrier beam 132 and control beam134. Graph 356–362 of groups 350, 352, and 354 are related to timedelays Δt=0, Δt<T, and Δt=T, respectively.

Time-delays Δt between information carrier beam 132 and control beam 134can be produced, for example, by control unit 214 of laser 210 as shownin system 200 of FIG. 6 b or by delay-fiber 306, as illustrated insystem 300 FIG. 7 b.

For graphs 356–362 of group 350, Δt=0, which means that the pulses ofinformation carrier beam 132, shown in graph 356, and the pulses ofcontrol beam 134, shown in graph 358, are in phase without any delaybetween them. In this case combined grating 100, in optical systems 200and 300 of FIGS. 6 b and 7 b, respectively, is irradiated on both of itssides simultaneously and acts as a grating having pitch d<λ.Accordingly, grating 100 produces interference pattern 150 having onlyone beam (interference order i=0) that is similar to the interferencepattern illustrated by graph 150A of FIG. 5. In such a situation and asexplained above in the description attending FIG. 6 b, the radiationintensities of carrier beam 132 and control beam 134 are emitted onlythrough port P₂, as shown by graph 360 resulting in a combined output ofzero, as illustrated by graph 362. Also, it is obvious that when theradiation intensity of both of beams 132 and 134 is zero, then theradiation intensities at ports P₂ and P₃ is also zero, as shown bygraphs 360 and 362, respectively.

For graphs 356–362 of group 352 Δt<T, which means that the pulses ofinformation carrier beam 132, shown in graph 356, and the pulses ofcontrol beam 134, shown in graph 358, have a time-overlap T10 betweenthem. Time overlapping T10=T−Δt. In this case, for the time period equalto T10, combined grating 100 in optical systems 200 and 300 of FIGS. 6 band 7 b, respectively, is irradiated on both of its sides simultaneouslyand acts as a grating having pitch d<λ. Accordingly, grating 100produces an interference pattern 150 having only one beam (interferenceorder i=0) that is similar to the interference pattern illustrated bygraph 150A of FIG. 5. For the time period of time-overlapping T10, andas explained above with reference to FIG. 6 b, the radiation intensitiesof carrier beam 132 and control beam 134 are emitted and together fromport P₂, as shown by graph 360. The radiation intensity in port P₃ iszero, as illustrated by graph 362.

For the time periods that differ from overlapping interval T10, thereare three situations:

(1) Carrier beam 132 is on and control beam 134 is off. (2) Carrier beam132 is off and control beam is on. (3) Beams, 132 and 134 are off.

For the first situation, grating 100, of FIGS. 6 b and 7 b is irradiatedsolely, by beam 132, only on the side that includes grating layer 106and thus behaves as a grating having pitch λ<d<2λ. This producesinterference pattern 150, which is similar to interference pattern 150Bof FIG. 5. As explained in the description to FIG. 6 b, intensity Iemitted from port P₂ is zero, as shown by graph 360. Part of theradiation intensity of carrier beam 132 is emitted from port P₃ asillustrated by graph 362.

For the second situation, grating 100 of FIGS. 6 b and 7 b isirradiated, solely by beam 134, only on the side that includes gratinglayer 108. Thus it behaves as a grating having pitch λ<d<2λ, whichproduces interference pattern 150 which is similar to interferencepattern 150B of FIG. 5. As explained in the description to FIG. 6 b, theintensity I emitted from port P₂ is zero, as shown by graph 360. Part ofthe radiation intensity of carrier beam 134 is emitted from port P₃ asillustrated by graph 362.

For the third situation, it is obvious that when the radiation intensityof both beams 132 and 134 is zero, in that case, the radiation at portsP₂ and P₃ is also zero as shown by graphs 360 and 362, respectively. Forgraphs 356–362 of group 354 Δt=T. This means that the pulses ofinformation carrier beam 132, shown in graph 356, and the pulses ofcontrol beam 134, shown in graph 358, have a time-overlap of T10 betweenthem equal to zero. Grating 100 is irradiated alternately either by beam132 on the side that contains grating layer 106 when beam 134 is off orby beam 134 on the side that contains grating layer 108 when beam 132 isoff. This case is equivalent to switching alternately between the firstsituation and the second situation described above for group 352 ofgraphs 356–362. The switching between the first and the secondsituations is done immediately. As described above for the first and thesecond situations, the intensity emitted from port P₂ is zero for bothof the situations. This is shown by graph 360, and part of the radiationintensities of beam 132 or beam 134 is emitted alternately from port P₃in the first or the second situation, respectively. Accordingly, theradiation intensity emitted from port P₂, shown by graph 360, is alwayszero and the intensity emitted from port P₃ is always constant, as shownby graph 362.

As discussed above, optical systems 200 and 300 of FIGS. 6 b and 7 b canbe operated as optical switches for switching the emitted radiationbetween ports P₂ and P₃ by changing Δt from zero to Δt=T and vice-versa.

In addition, optical systems 200 and 300 of FIGS. 6 b and 7 b can beoperated as optical modulators for producing very narrow pulses. Forexample, the width of the pulses emitted from port P₂, illustrated bygraph 360 of group 352 is T10 when T10=T−Δt. The pulse width T ofcarrier beam 132 or control beam 134 is the shortest that can beachieved with the technologies known today. When using Δt≈T, then widthT10 of the pulses emitted from port P₂ of systems 200 and 300 of FIGS. 6b and 7 b, respectively, approaches zero. This means that the pulses atport P₂ are much shorter than the shortest pulses than can be achievedwith present technologies. The frequency of the short radiation pulsesat port P₂ is equals to the frequency of the original longer pulses ofbeams 132 or 134.

Optical systems 200 and 300 of FIGS. 6 b and 7 b, respectively, can beoperated as optical modulators that act like optical differentiatorsystems. When optical systems 200 and 300 operate as a differentiator,their operation is similar to electrical differentiator circuits in thesense that in both types of differentiators, optical and the electrical,the short pulses are derived from wider pulses while maintaining theoriginal frequency.

Interference pattern 250 of FIGS. 6 a–7 b is produced when control beam134 passes through grating layer 106 when its pitch d satisfies λ<d<2λ.Accordingly interference pattern 250 includes three beams correspondingto interference pattern orders i=0, 1, and −1. The beams of interferencepattern 250 exist only when control beam 134 is on and thus they areillustrated in FIGS. 6 a–7 b, by broken lines, having the interferenceindices i=0, 1, and −1. Similarly, the beams of interference pattern 150have indices of interference orders i=1 and i=−1. They exist only whenone of beams 132 or 134 is on and the other beam (134 or 132,respectively) is off and thus are also illustrated in FIGS. 6 a–7 b bybroken lines. Thus, arbitrarily narrow pulses may be formed by feedingsuitably-timed pulses into the inputs of the foregoing devices.

FIG. 8 a schematically illustrates an optical system 400 that is similarto optical systems 200 and 300 of FIGS. 6 a and 7 a, respectively.System 400 of FIG. 8 a is differing from systems 200 and 300 of FIGS. 6a and 7 a, respectively, only in the way that control beam 134 isproduced. In system 200, laser 210 is controlled by control unit 214 toproduce control beam 134. Beam 134 in system 300 is produced by acoupling part of the radiation of information-carrier beam 132 fromoptical fiber 202 into optical fiber 304. The radiation that is coupledinto optical fiber 304 propagates and is guided along this fiber throughdelay-fiber 306 and is emitted, as control beam 134, from fiber 304 atits output through port P₅.

In optical system 400 of FIG. 8 a beam 132 emitted from the output ofoptical fiber 202 at port P₄ is converted, by lens 204, into wide beam132. Beam 132 propagates from lens 204 toward beam-splitter 406. Part ofbeam 132 is directed toward attenuator 208 and passes through thisattenuator. Beam 132 continues to propagate from attenuator 208 andenters block 104 to impinge on combined grating 100 on its side thatincludes grating layer 106. The other part of beam 132 is transmitted bybeam-splitter 406 as wide control beam 134 directed toward reflector402. Reflector 402 receives control beam 134 and reflects this beamtoward reflector 216 that reflects and directs beam 134 toward combinedgrating 100. Control beam 134 impinges on grating 100 on its side thatincludes grating layer 108. The rest of the optical paths of beams 132and 134, starting from combined grating 100 in system 400 of FIG. 8 a,are similar to the optical paths of beams 132 and 134, starting fromgrating 100 in systems 200 and 300, as illustrated in FIGS. 6 a and 7 aand described with reference thereto.

Interference patterns 150 and 250 are produced by beams 132 and 134, ina similar way, in all of the systems, systems 200, 300 and 400 asillustrated in FIGS. 6 a, 7 a and 8 a and explained above in theaccompanied explanation to FIGS. 6 a and 7 a. Thus the explanationsgiven above for similar features are not be repeated here.

Reflectors 402 and 216 may be connected at a point 408, and may beoriented at a right angle to each other to form a retro-reflector 410.Reflector 410 is arranged to move, along arrows 404, to adjust gentlythe length of the optical path between reflector 216 and combinedgrating 100 to provide phase-matching between beam 132, passing throughgrating 100, and beam 134 reflected from grating 100. The adjustment maybe made automatically or manually. In a functioning system, as discussedabove, a calibration process may be periodically followed to insure thephase matching is optimal and consistent. Note that in addition toregular calibration, adjustment may be made based on peak signaldetected using normal data throughput so that the system is continuouslyadjusted. Alternatively, an error condition may invoke a calibrationprocess. The error condition may be determined based on average energyor peak energy of an output (e.g., from P₃)

Intensity equalization of the radiation intensities of beam 132, whichpasses through grating 100, and beam 143, which is reflected fromgrating 100, may be achieved by adjusting the attenuation factor ofattenuator 208.

While retro-reflector 410 moves along arrows 404 it does not cause anyundesired lateral shifting of beam 134 as occurs in system 300, in whichmoving reflector 218 along arrows 308 causes movement of beam 134 alongarrows 310.

Large movements of retro-reflector 410 along any desired distance,oriented in the direction of arrows 404, changes the length of theoptical path between reflector 410 and grating 100 and thus produces atime delay Δt between control beam 134 and carrier beam 132. Anexplanation of how the amount of delay Δt affects interference patterns150 and 250 is given above with reference to FIG. 7 c.

FIG. 8 b illustrates same optical system 400 of FIG. 8 a, describedabove, with additional ports P₀, P₁, P⁻¹, P₂, and P₃ arranged to receiveinterference pattern 150 from coupling lens 226. Switching the emissionof the radiation of information carrier-beam 132 between ports P₂ and P₃of optical fibers 230 and 234 is achieved by changing interferencepattern 150 from three beams (three interference orders i=0, 1, and −1)to only one beam (interference orders i=0). The way in which the changeof interference pattern 150 dictates which of ports, P₂ and P₃, is theone that emits carrier beam 132 is similar to the way that isillustrated by FIGS. 6 b and 7 b and the attending discussion.

Retro reflector 410 produces a time delay Δt between control beam 134and carrier beam 132. The length of the delay Δt affects interferencepatterns 150 and 250 and thus dictates the switching state and thereforewhether the output is from port P₂ or P₃ (or neither). An explanation ofhow the delay Δt affects interference patterns 150 and 250 and thus theswitching between ports P₂ and P₃ is given above in the description ofFIG. 7 c and elsewhere.

FIG. 9 is another alternative design for a combination of a transmittingand reflecting grating 500 designed according to the invention. Thedesign is achieved by bonding block 105 to block 104. Blocks 105 and 104and their glue may have the same index of refraction, as explainedabove. Avoiding reflection of the radiation passes from block 104 to 105(and vice-versa) allows a complete transmitting of beams 132 and 134through openings 110. Lines 118, 122, and 123 have breaks 128, 124, and506 to indicate that the dimensions of combined grating 500 and are notproportional to the dimensions of blocks 104 and 105. In reality thedimensions of grating 500 may be much smaller than suggested by theillustration of FIG. 9.

When blocks 104 and 105 have the same refractive index and are bondedwith index matching glue, the refractive index on both sides of combinedgrating 100 is the same and equal to N1. Accordingly, by substitutingrefractive index N0 with refractive index N1 in Eqs. (11) and (12) weget the condition for maintaining phase-matching between beams 132 and134 all over the planes of grating 500:φ0=φ1=φ2=45°.

The same holographic and photolithographic techniques that producecombined grating 100 produce also combined grating 500. Grating 500contains grating layers 502, 106, and 108. Reflecting lines 504 and 116of grating layers 502 and 108 are centered along lines 114 of gratinglayer 106.

The above condition for angles φ0, φ1, and φ2 assures that there will bephase-matching between the radiation reflected from grating 500 and theradiation that passes through grating 500. This phase-matching ismaintained all over both sides of combined grating 500 that includesgrating layers 502 and 108.

Beam 132 passes through openings 110 of grating layer 106 of combinedgrating 500 and is reflected from mask stripes 504 of grating layer 502of combined grating 500. Similarly, beam 134 passes through openings 110of grating layer 106 of combined grating 500 and is reflected from lines116 of grating layer 108 of combined grating 500.

When only beam 132 is incident, part of it passes through grating layer106 of combined grating 500 to produce an interference pattern similarto interference pattern 150 of FIGS. 6 a–8 b. The other part of beam 132is reflected by grating layer 502 of combined grating 500 to produce aninterference pattern similar to interference pattern 250 of FIGS. 6 a–8b. When only beam 134 is incident, part of it passes through gratinglayer 106 of combined grating 500 to produce an interference patternsimilar to interference pattern 250 of FIGS. 6 a–8 b. The other part ofbeam 134 is reflected by grating layer 108 of combined grating 500 toproduce an interference pattern similar to interference pattern 150 ofFIGS. 6 a–8 b.

Grating layers 502, 106, and 108 all have pitch d that satisfies λ<d<2λ.Accordingly, when only one beam 132 or 134 is incident and the otherbeam (134 or 132, respectively) is not, the resulting interferencepatterns, such as 150 and 250 shown in FIGS. 6 a–8 b, and pattern 150Bshown in FIG. 5 result. Interference Pattern 150B has three exitinglobes corresponding to interference orders i=0, 1, and −1.

When both beams 132 and 134 are simultaneously incident, the part of theradiation of beam 134 reflected from grating layer 108 and the part ofthe radiation of beam 132 that passes through grating layer 106 producean interference pattern, such as interference 150 of FIGS. 6 a–8 b. Thecombination of grating layers 106 and 108 of grating 500 producesgrating with a pitch d that satisfies d<λ. Accordingly, in this case,the interference pattern is similar to interference pattern 150A of FIG.5 that has only one lobe corresponding to interference order i=0.

Similarly, when both beams 132 and 134 are incident simultaneously, thepart of the radiation of beam 132 reflected from grating layer 502 andthe part of the radiation of beam 134 that passes through grating layer106 produce an interference pattern such as interference 250 of FIGS. 6a–8 b. The combination of grating layers 106 and 502 of grating 500produces grating with a pitch d that satisfies d<λ. Accordingly, theinterference pattern is similar to interference pattern 150A of FIG. 5that has only one lobe corresponding to interference order i=0.

Combined grating 500 is symmetric with respect to beams 132 and 134 and,unlike combined grating 100, it produces interference patterns such as150 and 250 of FIGS. 6 a–8 b that are the same for any combination ofon-and-off of beams 132 and 134.

In FIGS. 6 a–8 b, when using combined grating 100, only the energy ofinterference pattern 150 is used, for switching and modulating purposes,and the energy of interference pattern 250 is lost. The use of combinedgrating 500 allows using two interference patterns, such as interferencepatterns 150 and 250 in FIGS. 6 a–8 b, for the same or similarapplications as shown in FIGS. 10–12 described below.

For clarity and without limitation, combined grating 500 is illustratedin a simple version that does not include transparent block 105. The twoversions of grating 500 are analogous to the two versions of grating 100in FIGS. 2 a and 2 b, without or with transparent block 105,respectively.

FIG. 10 a schematically illustrates an all optical modulating andswitching system 600 that is similar to optical system 300 of FIG. 7 bwith the following differences. Combined grating 100 in system 300 ofFIG. 7 b is replaced in system 600 of FIG. 10 a by the more efficientcombined grating 500 illustrated by FIG. 9. Radiation guides 610, 612and 624 collect the radiation of interference pattern 250, in system 600of FIG. 10 a. Unlike system 300 of FIG. 7 b, in which the radiation ofinterference pattern 250 is lost, system 600 collects the radiation ofinterference pattern 250 to be used in a manner similar to the way thatthe radiation of interference pattern 150 is used. Except for thesedifferences, the components of system 600, their arrangement, and theirmeans of operation are similar to those of system 300 of FIG. 7 b. Thusthe explanation for the similar parts of systems 300 and 600 is notrepeated.

As explained, grating 500 of FIG. 9 produces, with beams 132 and 134,interference patterns 150 and 250 that are the same and can be used forsimilar applications. For that reason, unlike system 300, in whichinterference pattern 250 is lost, in system 600 energy in interferencepattern 250 is collected by optical fibers 610, 612, and 624. Fibers610, 612, and 624 have corresponding ports P₁₀, P₁₁, and P⁻¹¹ at theirinputs to collect the beams related to interference orders i=0, 1, and−1, respectively. The radiation of interference pattern 250 propagatingfrom grating 500 is received by coupling lens 626 that couples thisradiation into ports P₁₀, P₁₁, and P⁻¹¹.

Optical fibers 610, 612, and 624, with their input ports P₁₀, P₁₁, andP⁻¹¹ and output ports P₁₂ and P₁₃, are used to collect the radiation ofinterference pattern 250. These ports are similar to optical fibers 230,232, and 234 with their input ports P₀, P₁, and P⁻¹ and output ports P₂and P₃ used to collect the radiation of interference pattern 150 ofFIGS. 6 b, 7 b, and 8 b.

Similarly, directional coupler 614 and phase-shifter 620 with itselectrode 622 are similar to directional coupler 224 and phase-shifter220 with its electrode 222, as illustrated in FIGS. 6 b, 7 b, and 8 b.All the components of FIG. 7 c are described above for the all-opticalswitching and modulating behavior of ports P₂ and P₃ including thebehavior that depends upon the time delay Δt. Pulse width T also appliesto ports P₁₂ and P₁₃.

The beams which have the interference orders i=±1 in both interferencepatterns 150 and 250 are indicated by broken lines to illustrate thatthese lobes disappear when both beams 132 and 134 incidentsimultaneously.

FIG. 10 b illustrates an upgrading unit 700 designed to collect theradiation energy of interference pattern 250 of systems 200 and 400 ofFIGS. 6 b and 8 b, when their grating 100 is replaced by grating 500. Asexplained above for grating 500 of FIG. 9, this grating produces, withbeams 132 and 134 interference patterns 150 and 250 that are the sameand can be used for similar applications. In systems 200 and 400 ofFIGS. 6 b and 8 b, respectively, the energy in interference pattern 250was lost. However when these systems are integrated with unit 700, theenergy in interference pattern 250 is not lost and is collected byoptical fibers 610, 612, and 624 of unit 700. Fibers 610, 612, and 624have corresponding ports P₁₀, P₁₁, and P⁻¹¹ at their inputs to collectthe beams corresponding to interference orders i=0, 1, and −1,respectively. The radiation of interference pattern 250 propagating fromgrating 500 is received by coupling lens 626, which couples thisradiation into ports P₁₀, P₁₁, and P⁻¹¹.

Optical fibers 610, 612, and 624 of unit 700, with their input portsP₁₀, P₁₁, and P⁻¹¹ and output ports P₁₂ and P₁₃, are used to collect theradiation of interference pattern 250. These fibers are similar tooptical fibers 230, 232, and 234 of systems 200 and 400, with theirinput ports P₀, P₁, and P⁻¹ and output ports P₂ and P₃. These fibers areused to collect the radiation of interference pattern 150.

Similarly, directional coupler 614 and phase-shifter 620 of unit 700,with its electrode 622, are similar to directional coupler 224 andphase-shifter 220 of systems 200 and 400, with their electrode 222, asillustrated in FIGS. 6 b, 7 b, and 8 b.

Graphs 360 and 362 of FIG. 7 c illustrate the all-optical switching andmodulating behavior of ports P₁ and P₂ of systems 200 and 400, includinghow this behavior is dependent upon time delay Δt and pulse width T. Theillustration of FIG. 7 c represents also ports P₁₂ and P₁₃ of unit 700.

The lobes of interference orders i=±1 in interference pattern 250 areillustrated by broken lines to show that these beams disappear whenbeams 132 and 134 are simultaneously incident. The resulting lobes arecoupled into ports P₁₁, and P⁻¹¹ by coupling lens 626.

FIG. 10 a already illustrates the integration of unit 700 with system300 of FIG. 7 b to produce system 600. The way unit 700 improves theefficiency of optical system 600 is described above in the explanationof FIG. 10 a. The improvement of systems 200 and 400 of FIGS. 6 b and 8b, by integrating unit 700, is achieved in a similar manner as thatillustrated in FIG. 10 a and described above and thus is not repeatedhere.

FIG. 11 a schematically Illustrates an optical system 800 for anall-optical switching and modulating system, including interferencedevice 801 made of groups of radiation guides 814 and 816. Informationcarrier beam 132 is optically coupled into ports P₄ at the inputs ofradiation guides 802 of bundle 804. The other sides 810, at the outputsof optical fibers 802, are optically coupled to inputs 813 of waveguides814. Waveguides 814 are one group out of two groups of waveguides 814and 816 that form interference device 801.

Similarly, control beam 134 is optically coupled into ports P₅ at theinputs of radiation guides 806 of bundle 808. The other sides 812, atthe outputs of optical fibers 806, are optically coupled to inputs 815of waveguides 816. Waveguides 816 are one group out of two groups ofwaveguides that forms interference device 801.

Waveguides 814 and 816 are interleaved such that one waveguide 816 islocated in each space between two waveguides 814 and vice-versa. Thedimensions of optical fibers 802 and 806 are relatively large; thus thespaces between waveguides 814 and 816 fit the dimensions of fibers 802and 806. The outputs of fibers 802 and 806 at their ends 810 and 812 arealso relatively large. Thus inputs 813 and 815 of waveguides 814 and816, respectively, are also designed to be large to allow efficientoptical coupling between fibers 802 and 806 and inputs 813 and 815 ofwaveguides 814 and 816, respectively.

Waveguides 814 and 816 at output 823 of device 801 are preferablyarranged in a very dense structure to assure that pitch d1 between twofollowing waveguides 814 or 816 satisfies λ<d1<2λ. Also the pitch d2between the two following waveguides 814 and 816 should satisfy d2<λ.

Note that the configuration of waveguides 814 and 816 changes from largewaveguides separated by large spaces, at input 817 of device 801, tosmall waveguides separated by small spaces at output 823 of device 801.This is achieved by bending waveguides 814 and 816 and changing theirsize by shaping them in a form of an adiabatic taper.

Device 801 can be made, for example, of silica, fused silica, diffusedglass, lithium niobate, liquid crystals, and semiconductors such assilicon, GaAs, AlGaAs, InP, InGaAsP, CdTe and CdZnTe. Device 801 is madeof substrate 820, which carries confinement layer 818 to guide theradiation. Layer 818 may have an index of refraction that is higher thanthe index of refraction of substrate 820. Growing epitaxial layers usingtechniques of Liquid Phase Epitaxy (LPE), Molecular Organic ChemicalVapor Deposition (MOCVD), and Molecular Beam Epitaxy (MBE) can producelayer 818. Diffusing dopants into substrate 820 can also produce layer818. For example, diffusion of Ag ions into lithium-niobate substrate820 can produce layer 818.

The fabrication of radiation waveguides 814 and 816 in layer 818 ofdevice 801 may be accomplished using standard IC industry etching andphotolithography techniques.

The radiation of information carrier beam 132 is coupled into ports P₄of fibers 802 of bundle 804 and exits from fibers 802 at their ends 810.This radiation is then coupled into inputs 813 of waveguides 814 atinput 817 of device 801. Waveguides 814 carry the radiation of beam 132to the output of guides 814 at output 823 of device 801. To avoid anydelay between the radiation from guides 814 at output 823 of device 801,the total length of all the optical paths between ports P₄ and theoutputs of guides 814 at output 823 are adjusted to be the same.Alternatively, any differences resulting in phase mismatching may becorrected using adjustable phase correction devices as discussed aboveand below. Phase-matching between the beams from guides 814 at output823 can be achieved by strong coupling between guides 814 to produce aneffect similar to phase lock. To produce more positive phase matchbetween the beams of guides 814, phase shifters 822 can be produced ontop of guides 814 by thin film techniques. The electrodes 824 and 826can control each of phase shifters 822 separately. Controlling phaseshifters 822 is done by applying control voltages to their electrodes824 and 826, which in turn changes the refractive index of guides 814and thus causes a phase shift of the radiation that they guide.

Maintaining equal intensity of all the beams that exit from guides 814at output 823 can be achieved by ensuring equal losses for all theoptical paths between ports P₄ and the output of guides 814 at output823. Alternatively, optical amplifiers 828 can be produced, on top ofguides 814, by thin-film techniques. Amplifiers 828 are controlledseparately through their electrodes 830 and 832 by applying controlvoltages. Thus the intensities of the beams in guides 814 at output 823can be controlled to be the same, by adjusting the amplifications ofamplifiers 828.

The radiation of control beam 134 is coupled into ports P₅ of fibers 806to be emitted from guides 816 at output 823 of device 801. This is doneanalogously to the way in which the radiation of information carrierbeam 132 is coupled into ports P₄ to be emitted from guides 814 atoutput 823 of device 801. In addition, the same control for the phases,the time delays, and the intensities described above for informationcarrier beam 132 propagating in guides 814 is applied to control beam134 propagating in guides 816.

Accordingly when the radiation of information carrier beam 132 iscoupled through ports P₄ of bundle 804 of fibers 802, it is divided andexits with the same intensity and phase. It does so from multiple guides814 arranged in every other guide in the combined group of guides 814and 816 at output 823 of device 801.

Similarly, when the radiation of control beam 134 is coupled throughports P₅ of bundle 808 of fibers 806, it is divided and exits. It doesso with the same intensity and phase, from multiple guides 816 arrangedin every other guide in the combined group of guides 814 and 816 atoutput 823 of device 801. The phases and the intensities of beams 132and 134 at the outputs of guides 814 and 816 are equal.

As indicated above, waveguides 814 and 816 at output 823 of device 801are arranged in a very dense structure to ensure that pitch d1 betweentwo successive waveguides 814 or 816 satisfies λ<d1<2λ. Also the spacingd2 between two following waveguides 814 and 816 should satisfy d 2<λ.

The group of waveguides 814 and 816 at output 823 of device 801 isactually a an array of radiation waveguides that act similarly tocombined grating 100, illustrated and explained above. Thus device 801acts as interference device similar to combined gratings 100 and 500.When only information carrier beam 132 or only control beam 134 is on,the combined group of guides at output 823 has a spacing d1 thatsatisfies λ<d1<2λ.

This means that when only information carrier beam 132 or only controlbeam 134 is on, device 801 produces interference pattern 150 similar tointerference pattern 150B of FIG. 5. The latter is producedby grating100, and has three lobes corresponding to interference orders i=0, 1,and −1. When beams 132 and 134 are simultaneously on, the combined groupof waveguides at output 823 has pitch d2 that satisfies d2<λ. In thiscase interference pattern 150 that device 801 produces is similar tointerference pattern 150A of FIG. 5, producedby grating 100, and havingonly one beam corresponding to interference order i=0.

Interference pattern 150 of FIG. 11 a is collected by coupling lens 226to couple the lobes of this pattern into the ports of an optical unit(not shown). This unit is similar to unit 700 of FIG. 10 b but does notinclude grating 500 and coupling lens 626. The latter converts device801 into all-optical switch and modulator.

FIG. 11 b illustrates an optical system 900 for all-optical switchingand modulating. System 900 is a combination of systems 800 of FIG. 11 aand 700 of FIG. 10 b. System 700 does not contain grating 500 orcoupling lens 626; the latter is replaced by coupling lens 226 of system800. System 900 produces interference pattern 150 of the types 150A or150B of FIG. 5 according to the on or off condition of beams 132 and134, as illustrated in FIG. 11 a and explained above. The operationalprinciple of system 700 is illustrated in FIGS. 6 b, 7 b, 8 b, 10 a and10 b and is explained in the attending discussion. System 700 receivesthe radiation of interference pattern 150 and emits this radiationalternatively from ports P₁₂ and P₁₃. When only beam 132 or only beam134 is on, then interference pattern 150 is of the type 150B,illustrated by FIG. 5, and only port P₁₃ emits the radiation ofinterference pattern 150. The latter is coupled to system 700 by lens226 into ports P₁₀, P₁₁, and P⁻¹¹. The radiation intensity at port P₁₂is zero.

Alternatively, when beams 132 and 134 are on simultaneously, theninterference pattern 150 is of the type 150A, illustrated by FIG. 5.Only port P₁₂ emits the radiation of interference pattern 150; thelatter is coupled to system 700 by lens 226 into ports P₁₀, P₁₁, andP⁻¹¹. Here the radiation intensity at port P₁₃ is zero.

The switching and modulating properties of system 900 are analogous tothose in FIG. 7 b. Accordingly, the switching and modulating behavior ofsystem 900 is a function of the pulse width T of beams 132 and 134 andthe delay time Δt between these beams. This is illustrated by FIG. 7 c.Control beam 134 can be produced , as shown in FIG. 6 b, by laser 210that is controlled by control unit 214. When laser 210 is turned on itis impossible to predict the phase of the its beam 134. Accordingly,this configuration has the disadvantage of the difficulty of controllingthe phase of beam 134 relative to beam 132. The configurations of FIGS.11 c and 11 d solve this problem.

FIG. 11 c schematically illustrates optical system 100, an all-opticalswitching and modeling system that is self-controlled . System 1000includes system 800 of FIG. 11 a with an additional illustration showinghow information carrier beam 132 and control beam 134 are produced .Information carrier beam 1002 is coupled into optical fiber 1004 throughits input 1001 and propagates inside fiber 1004 toward Y-junction 1005.In Y-junction 1005, the radiation of beam 1002 is divided intoinformation carrier beam 132 and control beam 134, which propagatesinside optical fibers 1006 and 1010, respectively. Beam 132 exits fromfiber 1006 at its output 1008. Beam 132 is collected and expanded , bycoupling lens 1022. It is coupled into ports P₄ of fibers 802. Beam 134propagates inside fiber 1010 through time-delayer 1012 and phase shifter1014 and exits from fiber 1010 at its output 1018. Beam 134 is collectedand expanded , by coupling lens 1020. It is then coupled into port P₅ offibers 806.

Time delayer 1012 produces a time delay Δt between beam 132 and 134.Phase shifter 1014 changes the phase of beam 134 to match the phase ofbeam 132. The delay time Δt, which time delay 1012 produces, dependsupon the extra length of its fiber loop. The voltage applied to controlelectrode 1016 of phase shifter 1014 controls the phase shift of beam134.

The operational principle of shifter 1014 is similar to that of shifter220 of FIG. 6 b. The optical paths of beams 132 and 134 from ports P₄and P₅, respectively, are similar to system 800 of FIG. 11 a. Sincebeams 132 and 134 are both derived from a single beam 1002, phaseshifter 1014 can maintain stable phase-matching between these beams.

FIG. 11 d schematically illustrates optical system 1100 for anall-optical switching and modeling system that is self-controlled .System 1100 includes system 800 of FIG. 11 a with an additionalillustration showing how information carrier beam 132 and control beam134 are produced .

Beam splitter 1104 divides wide information carrier beam 1102 intoinformation carrier beam 132 and control beam 134. Beam 132 is reflectedby splitter 1104 and is directed toward bundle 804 of fibers 802 to becoupled into ports P₄ of fibers 802. Beam 134 propagates throughsplitter 1104 toward retro-reflector 1106. Retro-reflector 1106 receivesbeam 134, from beam splitter 1104, and reflects beam 134 in the oppositedirection with a vertical displacement toward reflector 1108. Reflector1108 receives beam 134, from retro-reflector 1106, and reflects beam 134toward bundle 808 of fibers 806. It is then coupled into port P₅ offibers 806.

Retro reflector 1106 is arranged to move along arrows 1110 to change thelength of the optical path of control beam 134 between splitter 1104 andport P₅. Accordingly, the movement of retro-reflector 1106 along arrows1110 is used to control both the phase and the time delay Δt betweenbeams 132 and 134. While a gentle movement of reflector 1106 alongarrows 1110 controls the phase-matching between beams 132 and 134, alarge movement of reflector 1106 along arrows 1110 controls the delaytime Δt between beams 132 and 134. The above movements of reflector 1106along arrows 1110 maintain the orientation and the position in whichbeam 134 hits reflector 1108 and thus do not change the coupling of beam134 into ports P₅.

The optical paths of beams 132 and 134 from ports P₄ and P₅,respectively, are similar to what is illustrated by system 800 of FIG.11 a and described with reference thereto. Since beams 132 and 134 areboth derived from a single beam 1102, retro-reflector 1106 can maintainphase-matching between them that is stable.

FIG. 12 illustrates a modulator and switch 1200 representing anall-optical self-controlled switch that is activated by a predeterminedlogical code of digital pulses representing data in carrier beam 1210.Switch 1200 (alternatively referred to as modulator 1200) represents anyof the optical switches illustrated and described before. For example,switch 1200 includes and represent system 300 of FIG. 7 b when input1202 of switch 1200 couples optical fibers 1206 with fibers 202 ofsystem 300. Output 1204 of switch 1200 couples port P₂ of system 300with fiber 1208. Switch 1200 may be characterized by the parameters Tand Δt “(T, Δt)” in the drawing, where Δt is the time delay produced bytime delayer 306 of FIG. 7 b. The parameter T is the width of the pulsesthat switch 1200 receives at its input 1202 and T1 is the width of thepulses that switch 1200 produces at its output 1204.

Information carrier beam 1210 propagates in core 1214 of fibers 1206 andis coupled by input 1202 of switch 1200 to fibers 202 of system 300 ofFIG. 7 b. Beam 1210 is divided , by system 300, into two beams,information carrier beam 132 and control beam 134. Beams 132 and 134inside switch 1200 are phase matched and beam 134 is delayed by Δt withrespect to beam 132. Port P₂ of system 300 is coupled to fiber 1208 byoutput 1204 of switch 1200 to emit pulses from output 1216 of fiber1208. Port P₂ of system 300 produces pulses only when the pulses ofbeams 132 and 134 exist together. The pulse width T received by switch1200 is maintained at output 1216 of fiber 1216 to be equal to T1 onlywhen there is a complete time overlap between the pulses of beams 132and 134.

Graphs 1230 at the lower part of FIG. 12 show the pulse intensity Iversus time t. The scale of the intensity I is arbitrary. Graph 1218 isrelated to the data stream of information carrier beam 1210 and beam 132of system 300. Graphs 1220 and 1222 are related to the data stream ofcontrol beam 134 of system 300 and beam 1212 at output 1216,respectively.

The data stream of beam 1210, illustrated by graph 1218, includes twopairs of pulses. In each pair the pulses have a width T and areseparated by a time Δt. The pairs of pulses in graph 1218 are separatedby a guard interval T2. The intervals T2, Δt, and T satisfy theinequality, T2>Δt>T. The data stream of beam 132 of system 300 issimilar to the data stream of beam 1210; thus graph 1218 illustrates thedata stream of beam 132 as well.

Graph 1220 illustrates the data stream of beam 134 of system 300. Thisdata stream 134 is delayed by an amount Δt with respect to the datastream of beam 132 shown in graph 1218. Accordingly the first pulse ineach pair of pulses of beam 134 has a time overlap with the second pulsein each pair of pulses of beam in the input stream 132.

Graph 1222 illustrates the data stream of beam 1212 at output 1216 offiber 1208. The pulses of beam 1212 shown in graph 1222 are present onlywhen the pulses of beams 132 and 134, shown in graphs 1218 and 1220,respectively, exist simultaneously.

Accordingly switch 1200 is a self-activated all-optical switch.Information carrier beam 1210 arranged to include information pulses,each of which is followed by activating pulse at a time space Δt. Theinformation pulses, together with their respective (following)activating pulses defines a pair of pulses each of which may represent asymbol (e.g., a bit) and each of which is separated by time T2>Δt>T.Note that each symbol or pulse pair may, encode more than a single bit,for example by means of pulse amplitude modulation (PAM) or may bephase-encoded as well to provide phase-shift keying (PKM) or quadratureamplitude modulation (QAM) symbols.

Optical (T, Δt) emits, from output 1216, the information pulses alonewithout the activating (control) pulses. This emitting of theinformation pulses occurs only when the time delay Δt of (T, Δt) (switch1200) is equal to the time spacing between the information pulses andthe activating pulses related to each pair of pairs of pulses in beam1210.

FIG. 13 illustrates a group of graph 1300 demonstrating the principle ofall-optical self-triggered CDM according to the invention. Graphs 1302to 1310 of group 1300 illustrate the intensity I of ONE and ZERO logicalbits versus time t.

Graph 1302 shows time-envelope 1312 in which the logical data ofdifferent serial information channels can be placed. Time-envelope 1312does not contain any logical data; it shows only time slots 1314 inwhich pulses are allowed. Time-envelope 1312 is divided into equallength intervals T3. Each interval T3 contains a guard interval T2 thatis equal to or longer than T3/2. Guard interval T2 is a restricted timezone for any type of data and neither information nor control(activating or triggering) pulses are allowed during this period. A timeslot T4=T3−T2 is an interval during which data may be encoded. Timeperiod T4 is divided to K time pulse-slots 1314 having width T4/K=Δt.Each pulse-slot 1314 within envelope 1312 may contain a logical pulsehaving a width Δt.

As described with reference to FIG. 12, the code for activating opticalswitch 1200 of FIG. 13 includes a symbol representing data and anactivating (controlling or triggering) pulse. These pulses are separatedby a time interval corresponding to a data particular channel. Each ofthe information channels gets its identity by its specific code definedby the delay between the pulses making up the symbol. That is, the datafor each different channel differs from the others by the unique timemΔt between the pair of pulses representing specific code, where m is aninteger channel number. This method is a form of CDM with each pulsespacing defining a unique channel. Alternatively, each unique pulsespacing may represent a different data symbol.

Each time slot T4, with its pulse-slots 1314, may be reserved, in TDMfashion, for a TD channel or each time slot may be used for a singlechannel. For each time slot T4 only two pulses, each pair correspondingto one symbol, is provided in each slot T4. Since guard interval T2 isforbidden for any type of pulses, interval T3 can contain only twopulses as well.

Envelope 1312 of graph 1302 may contain multiple codes of multipleinformation channels interleaved serially with the time in any desiredorder.

For example, graph 1304 illustrates serial data stream 1322 includingpulse pairs 1316, 1318, and 1320 of three different TD channels. Pulsepairs 1316, 1318, and 1320 each include two pulses separated by times2Δt, 5Δt, and (k−1) Δt, respectively.

To demultiplex serial data stream 1322 of graph 1304 from a singleoptical fiber into multiple parallel ports of optical fibers, each mustcontain only one information channel corresponding to this port. Datastream 1322 may be split into multiple ports. To each port is appliedthe signal 1322. For example, the signal 1322 may be applied to theinputs of all-optical switch 1200 of FIG. 12. Switches 1200 eachcharacterized by a unique pair of parameters T and Δt.

Each of switches 1200 receives at its input 1202 the entire data streamincluding the codes of all the information channels. Each switch 1200detects and emits, at its output, pulses only for data in the input datastream code corresponding to the code channel for which the switch isconstructed. Thus, in this design, each of output ports 1204 of switches1200 will emit only the information pulses of one information channelfrom the serial of channels of graph 1304.

Graph 1304, illustrates data stream 1322. All switches 1200 receive thisdata stream at their inputs 1202. Thus this graph also illustrates thedata stream of beams 132 inside switches 1200, as described above in theexplanation of FIG. 12.

Graph 1306 illustrates data stream 1322 of graph 1304 with a time delayof 2Δt. As explained above for switch 1200, this graph may illustratethe data stream of control beam 134, inside switch 1200, with the switchhaving a delay of 2Δt. Thus it is characterized by the vector (T, 2Δt).In this particular case, since the pulses 1316, 1318, and 1320 have awidth T equal to Δt, the switches are characterized by: (Δt, 2Δt). Notethat strictly-speaking, the descriptor (T, Δt) is not fully acharacterization of the switch in that Δt merely constrains the choicesof T and T is chosen a priori for use with a given switch. The switchitself is characterized by its internal delay which is indicated fullyby Δt.

Arrows 1324 show that only the first pulse of code 1316 in graph 1306has a complete time overlap with the second pulse of code 1316 in graph1304. Graphs 1304 and 1306 also illustrate the pulses of beams 132 and134, respectively. This means that inside this specific switch 1200there is also a similar time overlap between the pulses of beams 132 and134. Thus, only the information pulse of code 1316 will appear at output1204 of switch 1200. Output 1204 is characterized by (Δt, 2Δt). Codes1318 and 1320 do not produce, in this switch, any time overlap betweentheir pulses in corresponding beams 132 and 134. Thus none of theirpulses appears in the output of switch 1200.

Accordingly, in general, switch 1200 has a delay 2Δt characterized by(Δt, 2Δt). Switch 1200 emits only the information pulse from thetwo-pulse code of the information channel. It does so only when thiscode includes two pulses that are separated by a time space 2Δt. Thepulses of other codes, separated by a time space equal to the integralnumber of Δt that differs from 2Δt, will riot be emitted by switch 1200and will not appear at its output.

Similar to graph 1306, graph 1308 illustrates data stream 1322 of graph1304 with a time delay of 5Δt. As explained above for switch 1200, thisgraph actually also illustrates the data stream of control beam 134,inside switch 1200 when this switch has a delay of 5Δt. Thus it ischaracterized by (T, 5Δt). In fact since the pulses also have a width Tequal to Δt, the switch is characterized by (Δt, 5Δt).

Arrows 1326 show that only the first pulse of code 1318 in graph 1308has a complete time overlap with the second pulse of code 1318 in graph1304. Graphs 1304 and 1308 also illustrate the pulses of beams 132 and134 inside switch 1200, characterized by (Δt, 5Δt), respectively. Thismeans that in this switch there is also a similar time overlap betweenthe pulses of beams 132 and 134. Thus, only the information pulse ofcode 1318 will appear at output 1204 of switch 1200, characterized by(Δt, 5Δt). Codes 1316 and 1320 do not produce any time overlap betweentheir pulses in corresponding beams 132 and 134. Thus none of theirpulses appear in the output of switch 1200 characterized by (Δt, 5Δt).

Accordingly, in general, switch 1200 has a delay 5Δt characterized by(Δt, 5Δt). It detects only the information pulse from the informationchannel whose code includes the two logical pulses that are separated bytime 5Δt. The pulses of other codes that are separated by a time equalto integral number of Δt that differs from 5Δt will not be detected byswitch 1200 and will not appear at its output.

Similar to graphs 1306 and 1308, graph 1310 illustrates data stream 1322of graph 1304 with a time delay of (k−1)Δt. As explained above forswitch 1200, characterized by (Δt, 2Δt) and (Δt, 5Δt), this graphactually also illustrates the data stream of control beam 134, insideswitch 1200 when this switch has a delay (k−1)Δt. Thus it ischaracterized by (T, (k−1)Δt). In fact since the pulses also have awidth T equal to Δt, the characterization takes the form (Δt, (k−1)Δt).

Arrows 1328 show that only the first pulse of code 1320 in graph 1310has a complete time overlap with the second pulse of code 1320 in graph1304. Graphs 1304 and 1310 also illustrate the pulses of beams 132 and134 inside switch 1200, characterized by (Δt, (k−1)Δt), respectively.This means that in this switch there is also a similar time overlapbetween the pulses of beams 132 and 134. Thus, only the informationpulse of code 1320 will appear at output 1204 of switch 1200,characterized by (Δt, (k−1)Δt). Codes 1316 and 1318 do not produce, inthis switch any time overlap between their pulses in corresponding beams132 and 134. Thus none of their pulses appear in output 1204 of switch1200 related to (Δt, (k−1)Δt).

Accordingly, in general, switch 1200, has a delay (k−1)Δt characterizedby (Δt, (k−1)Δt). It detects the information pulse only from theinformation channel whose code includes the two pulses that areseparated by time (k−1)Δt. The pulses of other codes are separated by atime equal to an integral number Δt that differs from (k−1)Δt. They willnot be detected by switch 1200, characterized by (Δt, (k−1)Δt), and willnot appear at its output 1204.

Accordingly, each switch 1200, out of all switches 1200 that are fed inparallel by the split information of the coded serial channels, willdetect only the information pulses from the code whose two pulses areseparated by a time equal to the delay of the switch. Thus switches 1200convert the serial coded channels propagating in a single optical fiberinto parallel channels, each of which propagates in different paralleloptical fibers.

While FIG. 13 illustrates only three channels represented by their codes1316, 1318, and 1320, the serial channels can contains k−1 differentchannels (for any desired k). These k−1 channels can be divided, asexplained above, from propagating in a single fiber to propagate inmultiple parallel fibers, each of which contains only the informationpulses from a different information channel.

Guard interval T2 is a forbidden time zone from which the logical pulsesare restricted. Guard interval T2 is needed to avoid unwanted timeoverlap between the pulses of different codes that exist in informationcarrier beam 132 and control 134 inside switches 1200. In a situationwhen guard interval T2 does not exist, the time delay between beams 132and 134 could cause time overlap between the pulses of different codesin beams 132 and 134. Such overlap could cause mixing and crosstalkbetween the divided different information channels propagating inparallel fibers, which should be isolated from each other.

Interval T3 contains only one pair of pulses and actually only one pulseof this pair represents an information pulse (or, put differently, eachpulse pair represents only one symbol). Interval T3 is at least 2 ktimes longer than the width Δt of the symbol. Accordingly, this methodof multiplexing may seem at first to be inefficient in terms ofinformation density. In practice, however, according to the inventionand as illustrated by FIG. 7 c and explained above in its description,the pulses can be produced with width T that is very narrow. Pulse widthT can be produced, according to the invention, to be so narrow thatinterval T3=2 k·T still will be much shorter than any pulse widthproduced by the modulators known today. Accordingly, a very dense serialstream of information channels can be used with the symbology method forwhat is here defined as Dense Time division Multiplexing\deMultiplexing(DTDM). The combination of the high density of information that can beachieved with the DTDM with the ultra high switching speed of thesymbology makes the use of the DTDM very attractive for use in opticalnetworks for transmitting a large volume of information at a high rate.

The optical system that actually performs the principle of thesymbology, illustrated by the graphs of FIG. 13, is illustrated by FIG.14, discussed below.

FIG. 14 schematically illustrates a self-triggered Code DivisionMultiplexing (CDM) system 1400 that is used for DTDM (Dense TimeDivision Multiplexing). Demultiplexing optical system 1400 is theoptical system that practically performs a CDM method based on thesymbology illustrated in FIG. 13. System 1400 has a single input 1402 towhich optical fiber 1408 is optically coupled. Information carrier beam1418 enters fiber 1408 through its input 1416 and propagates along fiber1408 to be coupled to system 1400 at input 1402. Input 1402 couplesinformation carrier beam 1418 into fiber 1403. Beam 1418 propagates infiber 1403 toward optical node (junction) 1406. Node 1406 can be aone-to-many coupler. It divides single information carrier beam 1418into k−1 information carrier beams 1420 that propagate along opticalfibers 1206. Each of beams 1420 contains all the information exists incarrier beam 1418. Each of fibers 1206 connects node 1406 to switch1200, which is of the type illustrated in FIG. 12 and which has input1202 and output 1204.

Switches 1200 are differ from each other only by their correspondingdelay parameter and thus are indicated by their correspondingparameters. The delay parameters of the (k−1) switches 1200 have valuesthat are integral number of Δt and create a series having serialdifferent Δt's that starting with Δt and endwith (k−1)Δt. Arrows 1410represents those of switches 1200 that are not shown in FIG. 14.

Information carrier beam 1418, propagating in a single fiber 1408,includes a serial data stream that includes k−1 different informationchannels interleaved between each other in any desired serial order.Beam 1418 has a time envelope 1312 (FIG. 13). Thus its pulses may occupyeach of time slots 1314 in time period T4 of envelope 1312 of FIG. 13 ina configuration that time period T2 is devoid of any pulse. Similar tograph 1304 of FIG. 13, the codes of the different information channelsare formed by their corresponding pairs of pulses. They are formed in aconfiguration where only one code is related to a specific informationchannel and exists during time period T4 of envelope 1312. Each codeincludes one information pulse and one control pulse for a single datasymbol.

The time lag between the two pulses of each of code is related to aparticular information channel. The time lag varies from one channel toanother and has a specific value that corresponds uniquely to arespective information channel. The interval between the two pulses ofthe (k−1) different codes have values that are integral multiples of Δtand define a series starting with Δt and endwith (k−1)Δt.

All the codes of the information channels that information carrier beam1418 carries arrive at inputs 1202 of switches 1200 through fibers 1206and by beams 1420 into which beam 1418 is divided. Beams 1420 carriesall the codes of the information channels that beam 1418 carries. Thesecodes are applied to switches 1200 via their respective inputs 1202.

Each of the switches 1200 detects and transmits to its output 1204 onlywhen the code in the information channel corresponding to its internaldelay. I.e., it only transmits pulses for the code corresponding to theparticular switch 1200 in which the pulses in each code are separated bya time interval equal to the time delay of the switch 1200. Neither theinformation pulse nor the activating pulse of the codes of otherchannels not corresponding to as given switch 1200 produces a pulse atthe its output 1204. Accordingly, the information pulses for each codeare output only by a respective information channel output 1412.

The information pulse of each code is represented by one of the twopulses that define the code. Each of switches 1200 receives, at itsinput 1202, various codes of different information channels. From thesevarious codes switch 1200 detects and transmits to its output 1204 onlythe information pulse of the code that is related to the specificinformation channel. In this case the time interval between the twopulses of the code is equal to the delay parameter of this specificswitch 1200.

For example, (k−1) optical switches 1200 are indicated by their (T, Δt),(T, 2Δt), (T, 3Δt), (T, 4Δt), and (T, (k−1) Δt). These switches willtransmit to their outputs 1204 only the information pulses from the(k−1) codes that correspond to that are separated by time intervalsequal to Δt, 2Δt, 3Δt, 4Δt, and (k−1)Δt respective thereto.

The information pulses of the different information channel are coupledby different outputs 1204 of switches 1200 into different fibers 1404and are carried by different beams 1414 that are from respective outputs1412 of system 1400.

Accordingly, optical system 1400 defines an all-optical Code divisionMultiplexing (CDM) system. System 1400 receives, in its single input1402, a series of multiple coded information channels interleaved in anydesired order. System 1400 emits, from its multiple outputs 1412, onlythe information pulses of the different coded information channels.These information pulses are fed into its input 1402, when each of thedifferent information channels exits, by a demultiplexing process, froma different output 1412 without any crosstalk between the channels.

FIG. 15 a illustrates how modulator and switch 1200 of FIG. 12 is usedto produce ultra narrow pulses 1508 of beam 1212 at output 1204.

Modulator 1200 receives in its input 1202, through optical fiber 1206,information carrier beam 1210 that is coupled to fiber 1206 into itscore 1214. Arrow 1506 indicates that pulse 1502 is related to beam 1210and has a width T. As explained above, beam 1210 is divided into carrierbeam 132 and control beam 134 inside modulator 1200. Carrier beam 132includes all the information of beam 1210 and thus pulse 1502 alsorepresents beam 132. Control beam 134 is delayed by a time delay Δt, asillustrated by pulse 1504 that is time shifted by Δt, relative to pulse1502 of beam 132, and has the same width T as pulse 1502.

The time overlap T−Δt between pulses 1502 and 1504 of beams 132 and 134,respectively, produce narrow pulse 1508 at output 1204 of modulator1200, that has a width T−Δt.

Pulse 1508 at output 1204 of modulator 1200 is coupled into opticalfiber 1208 and is emitted, by beam 1212, from fiber 1208 through itsoutput 1216, as is illustrated by arrow 1510.

The delay values Δt of modulator 1200 can be adjusted as desired andthus Δt can be chosen to produce pulse 1508 with an extremely narrowwidth T−Δt.

Accordingly modulator 1200 receives radiation pulses 1502 that can beproduced in a conventional way by conventional radiation sources andmodulators. These pulses are converted, by modulator 1200 into ultranarrow pulses 1508. These pulses are much narrower than the pulsesproduced by any known modulating technique.

Modulators, such as modulator 1200, can be placed in the optical path ofparallel information channels to convert their pulses into much narrowerpulses. Due to the narrow width of the new pulses in these parallelinformation channels, they can be interleaved to a serial data stream bystandard DTM techniques. This stream will have a much higher informationdensity, so as to produce DTDM. This serial pulse steam of the abovementioned DTDM should be demultiplexed by the fastest standardtechniques known today.

In addition to the DTDM, narrow pulses, such as pulse 1508 produced bymodulator 1200 or any other modulator according to the invention, canalso be used to increase the information density of any othercommunication method, such as WDM or DWDM.

The all-optical CDM according to the invention should have specialcodes. These codes should be encoded, by multiplexing, into the serialinterleaved data stream of the DTDM to allow the multiplexing by CDMtechnique of the invention. FIG. 15 b, described below, illustrates aninterleaving or multiplexing system according to the invention that isalso capable of encoding the symbols needed for the demultiplexing bythe CDM technique of the invention.

FIG. 15 b illustrates a system 1520 for encoding, by multiplexing, thespecific codes according to the invention, of multiple parallelschannels 1522 that are interleaved into serial data stream for TDM,DTDM, CDM, WDM, and DWDM, Asynchronous Transfer Mode (ATM), DenseAsynchronous Transmitting Mode (DATM), or any other application ofoptical communication, including packet routing.

System 1520 has multiple inputs 1526 and a single output 1528. Parallelinformation channels 1522, represented by their information pulses 1524,are fed into inputs 1526 of system 1520. Pulses 1524 are the shortestpulses that can be achieved today. Pulses 1524 are cut by lines 1530 toindicate that, in spite of their narrow width, their length is stillmuch longer than that illustrated.

Inputs 1526 of system 1520 are coupled into nodes 1532. Nodes 1532 thatreceive radiation pulses 1524 of channels 1522 divide this radiationequally into optical fiber 1534 and optical fibers 1536. The beams fromfibers 1534 and 1536 are fed into inputs 1202 of modulators 1200.

Modulators 1200 produce very short pulses 1544 at their outputs 1204.Each of pulses 1544 is accompanied by arrow 1545 that indicates in whichfibers pulses 1544 propagate. The width Δt=T−Δt1 of pulses 1544 dependsupon width T of pulses 1524 and delay time Δt1 of modulators 1200 ((T,Δt1). Modulators 1200 are arranged in (K−1) pairs, starting with pair1538 through pair 1540 to pair 1542. Broken arrows 1538 represent thepairs of modulators 1200 that are not shown in FIG. 15.

Pulses 1544 at outputs 1204 of modulator pair 1538 are coupled intooptical fibers 1546 and 1548, respectively. Pulses 1544 at outputs 1204of modulator pair 1540 are coupled into optical fibers 1550 and 1552,respectively. Similarly, pulses 1544 at outputs 1204 of modulator pair1542 are coupled into optical fibers 1554 and 1556, respectively.

Delay fibers 1558, 1560, and 1562 in fibers 1546, 1550, and 1556 producetime delays corresponding to the specific codes of modulator pairs 1538,1540, and 1542, respectively. For example, delay fibers 1558, 1560, and1562 produces delays of Δt, 2Δt, and (K−1)Δt, respectively. Index (K−1)represents the number of modulator pairs used when the (K−1)th pair ispair 1542.

Node 1564 receives pulses 1544, having width Δt, from fibers 1546 and1548. Node 1564 combines these two pulses and emits them, through singlefiber 1570, on the other side of node 1564. Pulses 1544 of fibers 1546and 1548 have a width Δt and are delayed by time interval Δt. Thus whencombined into fiber 1570, they produce a specific code pair 1576corresponding to modulator pair 1538, that includes two pulses that areshifted by Δt.

Node 1566 receives pulses 1544 from fibers 1550 and 1552. Node 1566combines these two pulses and emits them, through single fiber 1572, onthe other side of node 1566. Pulses 1544 of fibers 1550 and 1552 havewidth Δt and are delayed by interval 2Δt. Thus when they are combinedinto fiber 1572, they produce specific code pair 1578 corresponding tomodulator pair 1540, that includes two pulses that are shifted by 2Δt.

Similarly, node 1568 receives pulses 1544 from fibers 1554 and 1556.Node 1568 combines these two pulses and emits them through single fiber1574, on the other side of node 1568. Pulses 1544 of fibers 1550 and1552 have a width Δt and are delayed by time interval (K−1)Δt. Thus whenare combined into fiber 1574, they produce a specific code pair 1580,corresponding to modulator pair 1542, that includes two pulses that areshifted by (K−1)Δt.

Specific codes 1576, 1578, and 1580 of modulator pairs 1538, 1540, and1542 are accompanied by arrows 1582, 1584, and 1586 that indicate fibers1570, 1572, and 1574 in which they propagate, respectively.

Fibers 1570, 1572, and 1574 include delay fibers 1588, 1590 and 1592,respectively. Delay fibers 1588 to 1592 represent a series of (K−1)delay fibers corresponding to (K−1) modulator pairs 1538 to 1542. Thetime delays that delay fibers 1588 to 1592 produce are an integralnumber of time periods T3, shown in FIG. 13. These delays create amathematical series having a serial difference T3 that starts with adelay T3 and ends with a delay (K−1)T3 for first and last delays 1588and 1592, respectively.

Fibers 1570, 1572, and 1574 are connected to node 1594, which has only asingle output 1528 that is also the output of system 1520. The (K−1)specific codes 1576 to 1580 of the (K−1) information channels 1522 thatare coupled to (K−1) inputs 1526 of system 1520 propagate in (k−1)fibers 1570 to 1574. These codes enter node 1594 with time differencesT3 between them. Node 1594 combines (K−1) codes 1576 to 1580 into aserial data stream that consists of codes 1576 to 1580 that areinterleaved in every time period T3. Beam 1596 that exits from output1528 of system 1520 carries the serial data stream produced by node 1594that interleaves (k−1) codes 1576–1580 in serial of codes spaced by atime shift T3. Nodes 1564–1568 can be two-to-one couplers and node 1594can be a many-to-one coupler

Arrow 1598 indicates that the series of pulses that beam 1596 carries isrepresented by the pulses confined in time-envelope 1312, similar totime envelope 1312, illustrated in FIG. 13. Time envelope 1312 includestime cells 1602 having width T3 and defined as code cells 1602. Eachcode cell 1602 includes restricted time zones 1604 and occupied timezone 1606. The occupied time zone is a time period that can be used totransmit the codes pulses. The widths of restricted time zone 1604 andoccupation time zone 1606 are T2 and T4, respectively. Width T2 isgreater or equal to T3/2.

Any of occupation zones 1606 contains only one code out of (k−1) codes1576–1580. Since occupation zones 1606 may include any of (k−1) codes1576–1580, their size T4 must be great enough to allow them to containeven the longest code that has a width Δt(K−1)Δt=KΔt. Accordingly, thetime length of time zone 1606 is T4=KΔt.

Codes 1576–1580 are interleaved in (k−1) code cells 1602, where eachcode cell 1602 contains only one specific code related to its specificinformation channel 1522. Codes 1576–1580 are arranged in a series of(k−1) cells. These cells are arranged in a multiplexing or interleavingorder that starts with code 1578 and ends with code 1580. Specific codes1576–1580 are used in all-optical demultiplexing system 1400,illustrated in FIG. 14.

System 1400 receives cells 1602 and includes switches 1200 that producea time shift between their inside beams, carrier beam 132 and controlbeam 134. The maximum time shift between beams 132 and 134, insideswitches 1200 of system 1400, is illustrated by FIG. 14. It can reach avalue of (K−1)Δt. To avoid any mixing and crosstalk between the codes incells 1602, any time overlap between the different pulses of differentcodes 1576–1580 in cells 1602 of beams 132 and 134 should be avoided.Such over lap can be avoided if the separation time T2 between codecells 1602 is grater than the maximum shift (K−1)Δt between beams 132and 134 inside switches 1200 of system 1400. Accordingly T2 is equal toor longer than (K−1)Δt. Since T3=T2+T4, it is equal toKΔt+(K−1)Δt=(2K−1)Δt and thus T2 is approximately longer than or equalto T3/2.

The total length 1608 of all (k−1) code cells 1602 isT5=(K−1)T3=(K−1)(2K−1)Δt. When T2 is equal to T4=2kΔt, thenT5=(K−1)(2k)Δt. The time length T5 is the time that system 1520 of FIG.15 b is busy in producing code cells 1602. Thus system 1520 is free toget the next period of pulses, from information channels 1522 in itsinputs 1526, only after time period T5.

Accordingly, system 1520 operates at a frequency rate of 1/T5. The widthof pulses 1524 in information channels 1522 is much larger than thewidth of the pulses in codes 1576–1580. Thus there is a significant timesaving using the system of 1520 with respect to standard TDM system.

Compression Factor of DTDM With Respect to Standard TDM—FIG. 15 b

Compression factor C is defined as the ratio between the average bitrate exists in DTDM as, illustrated by FIG. 15 b, and conventional TDM,as used today.

According to the invention and as illustrated in FIG. 15 b, each codecell 1602, in the DTDM method, carries two pulses, but, assuming one bitper symbol for purposes of discussion, only, only one information bit.Accordingly, for a time period T5, that includes (k−1) codes cells 1602,the number of interleaved information pulses transmitted is (K−1). Thusthe average bit rate R1 in the DTDM is:R1=(k−1)/T5=(k−1)/[(k−1)(2K)Δt]=1/2KΔt

In a standard TDM the interleaved pulses, such as the pulses ofinformation channels 1522, have width of T. Thus for transmitting (K−1)pulses, the time needed is (K−1)T. Accordingly, the average bit rate R2is:R2=(k−1)/(K−1)T=1/T

Compression factor C equal to:C=R1/R2=T/2KΔt

For example, the width Δt of the pulses in codes 1576–1580 can easilyproduced to be 1000 times shorter than the width T of standard pulses,as produced and used in present TDMs. Assuming that K the number ofinformation channels interleaved in both methods DTDM and TDM is 50then:C=1000Δt/2·50·Δt=10

This means that, by using the DTDM method, the bit rate can easily beincreased by a factor of 10.

Achieving compression factor C=10, by the DTDM method with theadditional capability of ultra fast all-optical demultiplexing makes theDTDM a very attractive method.

When using DTDM with very short pulses, according to the invention, andinterleaving them, by the standard TDM method without encoding codes (asdone when using CDM), the compression factor C can be much higher. Theneed to encode the interleave pulses to be used, in all-opticalself-triggering CDM, reduces compression factor C significantly.

For example, when producing, according to the invention, pulses that are1000 times shorter than available today, by other techniques, andinterleaving them by a standard TDM technique, without CDM, thencompression factor C is 1000. On the other hand, such a high pulse ratecannot be demultiplexed using known techniques; demultiplexing by theCDM technique of the invention is required.

The all-optical switching capabilities of system 1400 of FIG. 14 are persingle code corresponding to a single information pulse. When the DTDMmethod is used to interleave packets of information, the code cells ofthe same packets are arranged in arrows, one after the other. All of thecells of the same packet have the same specific code and thus all willbe routed to the same port. Accordingly, all-optical demultiplexingsystem 1400 is also capable of routing packets. System 1400 can servesas one junction for routing packets. For routing packets through morethan one junction, the specific codes should include more information todefine the routing path through multiple junctions. Such codes will bediscussed in the following section.

FIG. 15 c schematically illustrates all-optical system 1700 representingan all-optical communication network. System 1700 includes system 1520of FIG. 15 b, that serves as an encoding or multiplexing system, andsystem 1400 of FIG. 14, described above, that serves as a demultiplexingsystem.

Systems 1520 and 1400 are connected by single long-haul fiber 1702 thattransmits a serial data stream of radiation pulses. A long haul is along information carrier designed to carry multiple information channelsfor transmitting large information volume, at high rate, betweenjunctions of the communication network. System 1520 has multipleparallel inputs 1526 through which it receives pulses 1524 of multipleparallel information channels 1522. Pulses 1524 are cut by lines 1530 toindicate that pulses 1524 are longer than as illustrated. System 1520produces specific codes corresponding to respective channels 1522; eachcode consist of a pair of pulses.

As illustrated in FIG. 15 b, these specific codes are all-opticallyinterleaved, by multiplexing system 1520, in any desired predeterminedorder to form series of code pairs 1596 that exit from system 1520through its output 1528. Data stream 1596 is coupled, by connector 1704,to a single long-haul fiber (backbone) 1702 through which it propagatestoward connector 1706. Connector 1706 couples data stream 1596 intoinput 1402 of demultiplexing system 1400.

As illustrated in FIG. 14, system 1400 receives the series of theinterleaved specific codes of channels 1522, produced by multiplexingsystem 1520, and all-optically demultiplexes only the information pulsesof these codes into and from its parallel outputs 1404. The informationpulses of the specific codes related to different information channels1522 are carried by beams 1414 and exit from different subsidiaryoutputs 1412 related to main outputs 1404 of system 1400.

Referring now to FIG. 16A, the mechanism for taking a (temporally) broadpulse 1337 or 1338, such as used in current optical systems, isprocessed to make the pulses much narrower. The resulting pulses may beinterleaved with appropriate delay circuits discussed below to create ahigh band width signal. Presently, the process for encoding abroad-pulse signal of the prior art to encode it with routing data forone or more layers of routing (e.g., layers of the system 1400) isdescribed. The system discussed now with reference to FIG. 16A is analternative to that discussed with reference to FIG. 15 b and is shownin the present context simply to illustrate another means by which thepulse-pair encoding may be achieved.

An input data stream 1340 is applied to an optical splitter 1341 whichmay be a directional coupler or Y-junction, to send energy in equalintensity to a gate 1352 such as described with reference to FIG. 12(there shown at 1200). It is assumed that the circuiting indicated bybroken lines in the diagram leading from the splitter 1341 to the gate,have appropriate delays such that the delay between the portion of thepulse arriving at one input of the gate 1352 is delayed by preciselyΔt_(C), a result that is schematically represented as a delay device(e.g., a delay line) at 1354. By applying each broad pulse 1337 and 1338to both inputs of the coincidence gate 1352 with a time delay Δt_(C),only the portion overlapping in time is transmitted to the output. As aresult, the output signal 1348 that emerges has a width Δt_(B) equal tothe difference between the delay Δt_(C) and original pulse width Δt_(D).The spacing Δt_(A) between the successive output symbols 1337′ and 1338′remains the same as in the original signal.

Each of many signals such as signal 1348 can then be applied to anoptical summing device, such as a Y-junction or other device (see belowfor discussion of Y-junctions, directional couplers, etc.) to create ahigh density time-multiplexed signal. Alternatively, an opticalamplifier can be used to amplify the signals either in their originalform 1338 or at a later stage after chopping and interleaving. WhileFIG. 16A shows a method of narrowing the pulses width, demultiplexing isa problem. This is addressed by encoding the signal in the mannerdiscussed with respect to FIG. 13. Encoding system 1520 illustrated byFIG. 15 b demonstrates an encoding process. Another means by which thisencoding may be accomplished is to route the pulses through multiplelayers, which is discussed with reference to FIGS. 16B to 16D.

The output signal 1348 from the previous figure may be applied to aduplicator circuit 1372. The latter is simply an optical splitter 1365and a delay device 1367 configured to split the signal 1348 and sum adelayed copy 1366 of the signal with a non-delayed copy 1364. Here thedelay is indicated as having a magnitude of Δt₃. The output signal 1362retains the original symbol spacing. As should be clear from theforegoing discussion and particularly that attending FIG. 14, when“routed ” by a receiving coincidence gate, the control/information pulsedisappears. To allow the pulse-pair to contain routing information formultiple layers, the pulse-pair must contain enough information to routethe pulses through the next layers in spite of the loss of pulses in therouting process through the previous layers. In this situation thepulse-pair contains multiple pulse-pairs and the original signal 1348 isreproduced in a corresponding channel by a repeating a process similarto that performed by duplicator 1372.

Note that the distance between adjacent pulses Δt_(A) is illustrated asbeing very large in this example. As discussed above, the allowed rangeof spacings between pulses, which corresponds to the number of degreesof freedom of the code, should preferably not violate the minimum guardband rule, unless some other means is employed to filter out unwantedinterference, a matter not discussed in the present disclosure. In thepresent example, the spacing Δt_(A) is illustrated as relatively largein anticipation of adding multiple layers of encoding, which isdiscussed next.

Referring now to FIG. 16C, the pulse-pair symbology may be applied tomultiple router layers of coincidence gate-based switches such as system1400 of FIG. 14. To accomplish this, the pulse pair encoding thedestination for a symbol is treated as a single pulse and reproduced, aswere the pulses of the original data stream 1348 in the descriptionattending FIG. 16B. The signal 1362 is applies to another duplicatorcircuit 1374 with another time delay Δt₂. This time delay Δt₂corresponds to the delay of a level of coincidence gate switch system(e.g. 1400) that would precede the switch layer configured to routebased on the time delay Δt₃. That is, Δt₃ Is the interval that specifiesa coincidence gate switch in the final layer of routing systems 1400 andΔt₂ is the interval that specifies a coincidence gate switch in thepenultimate layer of routing systems 1400. An upper layer of routingencoding may be added as illustrated in FIG. 16D. Here, each set ofpulses making up each symbol in signal 1366 is reproduced at anappropriate interval spacing by another duplicator circuit 1376configured with a delay of Δt₁. The encoding represented by the intervalΔt₃ would be the last to be processed and routed by the last layer(highest layer) of routing switch systems (e.g., 1400) that includesmultiple routing layers.

Referring now to FIG. 16E, signal 1368 is annotated with certain detailsto help clarify the above discussion. Each set of four pulses in theinterval 1384 represents a single symbol from the original source signal1340 encoded by the duplicator circuits 1372, 1374, and 1376. Each ofthe time intervals Δt₁, Δt₂, and Δt₃, selects a unique coincidence gateswitch (e.g. 1200 in a system including multilayer systems of FIG. 14)in a given layer of switch systems (e.g., 1400 in FIG. 14). Each outputof a switch, such as CDM system 1400, in a first layer, corresponds to aunique value of Δt₁. Each output of a switch in a second layer,corresponds to a unique value of Δt₂. Each output of a switch in a thirdlayer, corresponds to a unique value of and Δt₃.

The time slots available for encoding the highest layer codes range overan interval 1396. The slots are spaced at least a pulse width apart (andare at least a pulse-width wide). The series of adjacent slots must bedefined such that they occupy a time range that is no wider thaninterval 1396. A corollary is that Δt₃ should never be outside this timerange 1396.

The time slots available for encoding the penultimate layer codes rangeover an interval 1394. The slots are spaced apart by at least theinterval 1396. The slot widths are at least at least the interval 1396.The series of adjacent slots must be defined such that they occupy atime range that is no wider than interval 1394. A corollary is that Δt₂should never be outside the time range 1394.

The time slots available for encoding the antepenultimate or initiallayer codes range over an interval 1392. The slots are spaced apart byat least the interval 1394. The slot widths are at least at least theinterval 1396. The series of adjacent slots must be defined such thatthey occupy a time range that is no wider than interval 1392. Acorollary is that Δt₁ should never be outside the time range 1394.

A guard interval 1390 must maintain a distance between adjacent initialswitch layer slot ranges that is at least as great as interval 1392 toprevent intersymbol interference. The guard zone requirement only existsat the highest layer of encoding. This is because the time delays thatcorrespond to the lower layers is always a fraction of those at higherlayers, the presence of the highest level guard interval 1390 guaranteesthat no overlap will occur between successive symbols in the lowerlayers.

Refer now to FIG. 16F, which illustrates further how the multilayersignal is processed through multiple layers. The original signal (e.g.1368 from FIG. 16D) here shown at 1605, is applied to a first layer 1601of switches 1200A–1200F each with a respective time delay Δt_(a)−Δt_(f).Switch 1220C, which is within the range of switches 1200A–1200F (a rangewhich has an arbitrary number of switches within the confines of theencoding range), outputs signal 1606 because it is configured for thematching time interval Δt₁. The signal 1606, may be thought of ascontaining the structure of one half of the signal 1605 and results dueto the coincidence effect described for coincidence gates above. Theother switches in the layer 1601 output no signal, because their timedelays have non-matching values.

Signal 1606 is applied to the second layer of switches 1200N–1200R, eachwith a respective time delay Δt_(n)−Δt_(r). Switch 1220P, which iswithin the range of switches 1200N–1200R (a range which also has anarbitrary number of switches within the confines of the encoding range),outputs signal 1607 because it is configured for the matching timeinterval Δt₂. The signal 1607, may be thought of as containing thestructure of one half of the signal 1606 and results due to thecoincidence effect described for coincidence gates above. The otherswitches in the layer 1602 output no signal, because their time delayshave non-matching values.

Signal 1607 is applied to the third layer of switches 1200V–1200Z, eachwith a respective time delay Δt_(v)−Δt_(z). Switch 1220X, which iswithin the range of switches 1200V–1200Z (a range which also has anarbitrary number of switches within the confines of the encoding range),outputs signal 1608, because it is configured for the matching timeinterval Δt₁. The signal 1608, may be thought of as containing thestructure of one half of the signal 1607 (or a single pulse) and resultsdue to the coincidence effect described for coincidence gates above. Theother switches in the layer 1603 output no signal, because their timedelays have non-matching values.

Note that in FIG. 16F, the shapes of the pulse patterns are notnecessarily to scale.

FIG. 17 illustrates how WDM may be combined with the symbology method ofthe present invention in a communications system. Multiple instances ofthe interleaving/multiplexing system described with reference to FIG. 15b may be provided, for example as indicated at 1610. Each of themultiplexed channels may be assigned a frequency channel and multiplexedin a WDM process 1620 for transmission on a long haul channel 1615.Corresponding demultiplexing provided by a WDM demux engine 1625 isprovided at a receiving end, the respective frequency channels of whichmay be applied to respective optical demultiplexers 1626 and 1627, suchas those illustrated in FIG. 14. Note that two layers of demultiplexersare shown. These may employ the mechanism for multiple-layer encodingdescribed with respect to FIGS. 16A–16D.

There are several conclusions and ramifications regarding the details ofthe above embodiments that may be summarized here before discussing someother types of interference devices that may be configured to providecoincidence gate-type functionality similar to that discussed above. Oneof ordinary skill will observe that among the embodiments and inventionsdiscussed, at least the following are provided :

-   -   1. All-optical modulators for generating ultra narrow pulses to        produce DTDM.    -   2. Ultra fast all-optical switches.    -   3. All-optical modulators and switches that are radiation        controlled or are self-triggered.    -   4. All-optical encoding symbology that may be used for data        interleaving or multiplexing with very narrow pulses that may be        radiation controlled or self-triggered.    -   5. All-optical decoding or demultiplexing systems that may be        radiation controlled or self-triggered.    -   6. Extremely fast all-optical systems for multiplexing and        demultiplexing and which may be used for DTDM.    -   7. Extremely fast all-optical systems for multiplexing and        demultiplexing codes for CDM, self-routing, self-triggering,        ATM, and data routing.    -   8. A method for modulating logical symbols that are self-routing        without separate control data or packet headers.    -   9. Novel devices that may be used for selectively directing        optical energy in cylinders within and outside the        communications field.

The foregoing embodiments are by no means the only means by which theinventions discussed above may be implemented. Referring now to FIG. 18,as will be discussed in some detail below, directional couplers, asillustrated for example at 1650, are interference devices of a sort inthe radiation applied to them interferes to produce various results attheir outputs. For example, respective light signals applied to theports indicated at 1 and 2 may interfere in a way that is determined bythe structure of the directional coupler 1650. The interaction of thesesignals dictated by the structure of the coupler, the phase and electricfield amplitude of the light incident on the ports 1 and 2 (as well asother factors) determines the electric field amplitude and phase of thelight emitted from ports 3 and 4.

As will be appreciated by persons of skill in the relevant fields, it ispossible to create a directional coupler in which light incident on port1 will result in radiation signals being emitted from ports 3 and 4which are equal in electric field amplitude with a π/2 phase difference.More specifically, where the signal incident on port 1 has an electricfield amplitude of E, the signal emitted from port 3 would have anelectric field amplitude of E/√{square root over (2)} and in a certainphase relative to the input signal. The signal emitted from port 4 hasthe same field amplitude, but its phase is π/2 radians ahead of that ofthe signal emitted from port 3. The intensity of the signals is given bysquaring the electric field amplitude so the port 1 signal has intensityI=E², and port 3 and 4 signals have intensity I/2=E²/2 or half that ofthe signal applied to the input port 1.

For convenience, the following notation convention will be adopted. Theintensity of light will be specified and where relevant, the phaseindicated by multiplication by a symbol J to indicate a π/2 phasedifference, by −1 to indicate a π phase difference, and by −J toindicate a −π/2 phase difference. Thus, −J*I/2 means a signal whoseintensity is I/2 and whose phase is −π/2 ahead (or π/2 behind) of areference signal.

A quick review of the signals incident on waveguides 1655, 1660 showsthat when a signal is applied at port 2, the mirror-image obtains at theoutput ports 3 and 4. That is, the signal at port 3 is J*I/2 and that atport 4 is I/2. The more interesting situation occurs when light of equalintensity is incident on ports 1 and 2, but different in phase by −π/2.That is, the signal incident on port 1 is I and that on port 2 is −J*I.The output at port 4 is zero. All of the energy incident on ports 1 and2 arrives at port 3. In this case, although shown, the phaserelationship between the energy at port 3 and that at port 4 isirrelevant since no light is emitted from port 4.

Referring now to FIG. 19, the effects of reverse Y-junctions on inputenergy is discussed. When a light signal is applied to port 5 or 6 ofY-junctions 1680 and 1685, respectively, the output intensity at port 7is half that of the applied at the input. When light is incident on bothinput ports 5 and 6, of Y-junction 1690, simultaneously and in the samephase, the output energy output at port 7 is half the total applied atports 5 and 6. In terms of the phase effects, where input signalsinterfere so that input signals of opposite phase cancel each other andsignals in phase add, with a 50% attenuation in intensity.

Referring to FIG. 20, coincidence devices 1700 and 1705 are each formedfrom a pair of Y-junctions 1715 and 1730 and Y-junctions 1720 and 1760and a single directional coupler 1710 and 1725. Each device 1700 and1705 has a phase shifter 1740 and 1745 at a corresponding output port 7of each device 1700 and 1705. As may be determined by inspection, anidentical signal at ports 1 and 5 of intensity I results in a signal atport 7 of I/2 and signals of equal intensity at ports 3 and 4, with thesignal at port 4 being shifted forward in phase by π/2 relative to theothers. A −π/2 phase shift is applied to the port 7 signal resulting ina signal of −J*I/2, which is of the same magnitude as the port 4 signalbut opposite in phase. This is applied at port 9 of Y-junction 1730. Theport 4 signal is applied to port 8 of the same y-junction resulting inan output of zero at port 10.

The coincidence device 1705 experiences a similar cancellation effectwhen signals of J*I and I are applied at ports 2 and 6, as may beconfirmed by inspection and with the aid of the symbols in FIG. 20.Thus, when these inputs are applied at the ports 2 and 6, a zero outputis obtained at the output port 10. Referring now to FIG. 21, when thesignals of FIG. 20 are applied to all the input ports 1, 2, 5, and 6,simultaneously, a very different result obtains, with the result beingan output of intensity and phase J*I/2.

FIG. 21 shows that port 4 carries a signal of high intensity, with,namely an intensity of 2*I with a phase of π/2 as it enters port 8 ofY-junction 1785. The intensity at port 9 of Y-junction 1785, after thephase shifter 1780, is I with a phase that is opposite to that of thesignal in port 8. The Y-junction 1785 combines the powers in ports 8 and9 according to their intensities and phases to produce an output signalat port 10 with an intensity of I/2. At the same time, under the aboveconditions, nulling port 3 has zero output signal and all the energyfrom port 3 is transferred to port 4. It can be seen that the ratiobetween the intensities of port 4 in FIG. 21 and FIG. 20 is 4(2I/(I/2)=4).

Note that the notation in the drawings does not follow strictconvention. For example, the result obtained at port 10 is shown as amixture of intensity, which a scalar, and phase, which is a vector. TheY-junction 1785 may be configured, as is known in the art, so that itsoutput is half the sum of the intensities of its inputs with phasecancellation given by the interference of their waveforms. This meansthat where the inputs are opposite in phase, as is the case for inputsat ports 8 and 9, the output signal intensity is the difference of theinputs signal intensities attenuated by 50%. Where the input signals arein phase, the output is the sum of the intensities of the input signalsattenuated by 50%.

Note that the coincidence devices 1710, 1705, and 1770 may bemanufactured on a single substrate as waveguides. The phase shifters1740, 1745, and 1780 may be provided by simply heating a portion of thewaveguide material to change the refractive index. This could be donewith an ohmic heater or the like. Another way of forming the phaseshifters is to apply a voltage that creates a depletion region, a deviceknown as a Schottky contact. If the devices are made from opticalfibers, a pressure could be applied, for example, by means of apiezo-electric device, to change the index of refraction.

Note also that it should be obvious that some phase change will occur asenergy propagates along the waveguides in the forgoing devices. And thishas been ignored in the discussion. So, for example, the phase of thesignal output at port 4 will not be identical to the phase as the samesignal is applied to port 8. Similarly, the phase difference between thesignal at port 7 will not be precisely −π/2 radians different from thatat port 9. Thus, the discussion has discussed the performance of thedevices in a somewhat schematic way, but in a real device a designerwould have to account for propagation delays and the effect these haveon phase to insure that the desired results provide a coincidence effectsuch as that shown. In practice, this issue is a design detail that maybe ignored for purposes of discussion of the inventions and variousembodiments thereof.

Note that the light applied to one pair of ports (either 1, 5 or 2, 6),may regarded as a single signal input. The signal applied at the port 1,5 input is different, but equal in power to that applied to the port 2,6 input. The latter is an ordered pair with a predefined phasedifference that is always the same. When a signal is applied to oneinput without simultaneous application of a signal at the other, theoutput signal (port 10) is zero. When respective signals are applied atboth inputs, the output is equal to one fourth the power at either inputor an eighth of the total power applied to the inputs.

Because the port 2, 6 input has a predefined phase difference from thephases of the other input signals, and because of the behavior of thecoincidence device 1700, 1705, and 1770 noted above, it is possible toconstruct coincidence gate with behaviors that are similar to that ofembodiments shown in FIG. 6 b (an externally-triggered gate), forexample and 1200 of FIG. 12 (a self-triggered gate).

Referring now to FIG. 22, a self-triggered coincidence gate shown in acoincidence state where an input signal applied at input port 12 has apair of pulses separated by a time interval that matches delay lines1800 and 1801. The structure shown in FIG. 22, may be confirmed byinspection, to apply input signals to ports 1, 2, 5, and 6, that areidentical in terms of relative magnitude and phase to the signalscorresponding to the coincidence state illustrated in FIG. 21. If thetime interval Δt of the input signal applied at port 12 fails to matchthat of the delay lines 1800 and 1801, it may be confirmed by inspectionthat the result will be successive states of the system that coincidewith those illustrated in FIG. 20. The two possible noncoincidencestates obtain when the Δt of the input signal is different from that ofthe delay lines 1800 and 1801. In such cases, each pulse travels thoughthe gate 1810 without a corresponding pulse interfering with it inrelevant portions of the circuit as may be seen by inspection. That is,as illustrated in FIG. 23 when the first pulse passes through, passesthrough, a signal of intensity I passes through port 6 and one of J*Ithrough port 2′ (which corresponds to port 2 in FIG. 20) with nocorresponding pulse in ports 1 and 5. The result is the situation of thelower half of FIG. 20 where the output is zero. As illustrated in FIG.24, when the second pulse passes through, a signal of intensity I passesthrough ports 1 and 5 with no corresponding pulse in ports 2 and 6. Theresult is the situation of the upper half of FIG. 20 and the output iszero.

Note that although delay lines 1800 and 1801 (as well as delay lines andother devices illustrated in embodiments discussed below) areillustrated as elongated channels (E.g., in the present figure they aresuggested to be rolls of optical fiber, for example), various techniquesmay be used to produce the required delay. For example, materials inwhich light propagates more slowly (e.g., higher index of refractionachieved by doping) may be added so that the path need not be undulyelongated. Even some kind of energy conversion process likeoptical-electrical-optical could be used if delays are permitted to berelatively long. Such a device would act as a store-and-forward bufferbut with current energy conversion technology, it would be usable foronly very long delays. However, there some applications would permitthis.

Referring to FIG. 25, a design essentially the same as that of FIGS.22–24 may be based on the use of a star-splitter 1840 rather than threeY-junctions as in the embodiments of FIGS. 22–24. The lengths of theradiation guides arms of star-splitter 1840 are preferably designed toassure that the all the radiations enters the ports 1, 2, 5, and 6 withthe same phase (or equivalently such that the phase at which the enterthe points is appropriately compensated further on such that theultimate result of a coincidence-gate function is obtained). It shouldbe clear from the illustration that such an embodiment would behave in amanner that is equivalent to the embodiments of FIGS. 22–14.

Thus, it is clear that the behavior of the coincidence gate 1810 isessentially the same as that of gate 1200. However, the total energyloss of the gate 1810 may be substantially higher than that of gate1200. We assumed in the above discussion that the gate 1200 is based onthe embodiments of FIGS. 1–11 d, although the discussion of gate 1200and the modulation techniques discussed in connection with FIGS. 12–17apply equally to embodiments such as gate 1810 and other embodiments tobe discussed below.

Referring now to FIG. 26, another self-triggering coincidence gate-typedevice illustrates some concepts that may be used for making devicesbased on waveguide technologies and also some more general concepts. Forexample, a gate could be fabricated using lithography techniques usingsuch an approach. For example time delays may be provided in appropriatelocations with an alternative to the fiber optical delay lines suggestedby the images of delay devices 1800 and 1800 and 1801 of FIG. 22.Instead, a delay line, preferably of high-refractive index material, inthe form of an elongated waveguide achieved by, for example, serpentinepath portions 1905 and 1910 of the circuit, may be provided asindicated. These portions may be of a material with a higher index ofrefraction than the material used in other parts of the device so thatthe lengths of the serpentine paths portions 1905 and 1910 may beminimized for convenience. However, this is not necessary.

Another feature of the disclosed embodiment is that instead of usingY-junctions, star splitter, or a star coupler, a series of 50%/50%directional couplers 1920, 1925, and 1930 (known also as 3 dB couplers)are used in a manner similar to that of the embodiments of FIGS. 22–24.In this case, however, the directional couplers inherently introduce arelative phase difference of π/2 radians in the outputs which must beaccommodated in the design. In the schematic illustration, the signal atport 2 differs in phase from that at port 1 (when simultaneous signalsplace the device in the coincidence state) without the need for anadditional phase shifter.

Recall that these are only schematic illustrations and in practice, thestructure of the design (including path lengths and materials) mayinherently provide the phase shifting. For example, the serpentine delayportion 1905 or other types of delay devices such as delay lines 18001and 1801 (shown in FIG. 22), introduces multiple phase rotations and ifdesigned to do so, can insure that the correct relative phase angles areprovided at the various interference portions of the devices to obtainthe desired result.

Note also that there is another phase rotation introduced by directionalcoupler 1930 and yet another by directional coupler 1925. The end resultis that to achieve the desired interference effect in the coincidencedevice portion 1930 (i.e., the relative phase angles at the input ports1, 2, 5, and 6), a phase rotation of −π/2 radians is applied in thelower branch 1916 of directional coupler 1925. The result is that theinputs at ports 1, 2, 5, and 6 produce the constructive interferenceeffect at port 4 so that all the energy applied at ports 1 and 2emanates at port 4, but the phase angles emitted at port 7 needs to berotated by −π, before being applied to the Y-junction 1945 in order toproduce the coincidence-type output at port 10. Note that only thecoincidence state is shown in connection with the embodiment of FIG. 26,however it may be confirmed by inspection that the structure producesthe correct behavior under noncoincidence conditions.

Note that the use of directional couplers instead of Y-junctions resultsin a lower energy loss through the entire system. That is, one may besee that the energy loss through the embodiment of FIGS. 22–24 is afactor of 32, while the energy loss through the embodiment of FIG. 26 isonly by a factor of 8. The losses in the device of FIG. 26 may becompensated for by an optical amplifier 1950 at input port 1965.

Referring now to FIG. 27, another alternative mechanism for creating acoincidence gate device is illustrated here. A star splitter 1960 isconfigured to output an input optical signal applied at input port 1965to each of four ports 1970 with equal intensity and phase. The travelingtime from the input port 1965 of star splitter 1960 to each port of thepair of ports 1 and 5 (of ports 1970) is assumed in this example to bethe same. Similarly, The traveling time from the input of star splitter1960 to each port of the pair of ports 2 and 6 (of ports 1970) is alsoassumed to be the same. The energy loss with the star splitter 1960 isless than with the cascade of Y-junctions of the previous embodimentwith the input energy being equally divided among the outputs. As knownby those of skill in the relevant arts, such a structure may be createdvia current design techniques. In the embodiment of FIG. 27, serpentineportions are used for delay as in the embodiment of FIG. 26. In allother respects, the embodiment of FIG. 27 is essentially as theembodiment of FIG. 25.

Note that although in the embodiment of FIG. 27, the time delay of allthe branches of the star splitter 1960 was assumed to be the same, inpractice this, of course, need not be true as long as the coincidenceeffects required are obtained. For example, the delays of time delayers1967 and 1968 may be incorporated totally or in part in correspondingbranches of the star splitter 1960.

It should be clear from the above that there are a wide variety of waysof generating the coincidence-gate functionality from directionalcouplers and/or Y-junctions in various combinations.

Referring now to FIG. 28, another way to form a coincidence gate typefunctionality is by the use of certain features of beam splitters.Illustrated in FIG. 28 are dielectric beam splitters which have thefollowing properties. An incident beam 2010 incident in a firstdirection on a dielectric beam splitter 2025 is divided into a reflectedbeam 2015 and a transmitted beam 2020, each with an intensity that ishalf that of the input beam. The phase angle of the reflected beam 2015is π/2 greater than that of the transmitted beam 2020. The samesituation obtains when an incident beam 2030 is incident from anotherdirection on the dielectric beam splitter 2025. That is the incidentbeam 2030 is divided into a reflected beam 2035 and a transmitted beam2040, each with an intensity that is half that of the incident beam 2030with the phase angle of the reflected beam 2035 being π/2 greater thanthat of the transmitted beam 2040.

When incident beams 2010 and 2030 are coincident from their respectivedirections on the dielectric beam splitter 2025, with the indicatedphase relationships, they interfere constructively. The result is acoincidence effect at the output beam 2045 from the reflection directionof incident beam 2010 and the transmitted direction of incident beam2030. That is, in the reflection direction of incident beam 2010 and thetransmitted direction of incident beam 2030, the combined energy outputis four times that when either of the incident beams 2010 and 2030 isincident by itself.

The coincidence effect can be used to generate zero and non-zero outputsin noncoincident and coincident states, respectively by providingoptical circuits that provide a magnitude slicing function as providedin previous embodiments discussed above. A number of examples arediscussed below with regard to FIGS. 34–42. First, a few more examplesof coincidence devices are discussed.

Referring now to FIG. 29, metallic beam splitters have the followingproperties. An incident beam 2050 incident in a first direction on ametallic beam splitter 2025 is divided into a reflected beam 2055 and atransmitted beam 2060, each with an intensity that is a quarter that ofthe input beam. The phase angle of the reflected beam 2055 is π greaterthan that of the transmitted beam 2060. The same situation obtains whenan incident beam 2070 is incident from another direction on the metallicbeam splitter 2065. That is the incident beam 2070 is divided into areflected beam 2075 and a transmitted beam 2080, each with an intensitythat is a quarter that of the incident beam 2070 with the phase angle ofthe reflected beam 2075 being π greater than that of the transmittedbeam 2080.

When incident beams 2050 and 2070 are coincident from their respectivedirections on the metallic beam splitter, with the indicated phaserelationships, they interfere constructively and no loss occurs in themetal film (not shown separately). The result is a coincidence effect atthe output beam 2085 from the reflection direction of incident beam 2050and the transmitted direction of incident beam 2070. That is, in thereflection direction of incident beam 2050 and the transmitted directionof incident beam 2070, the combined energy output is four times thatwhen either of the incident beams 2050 and 2070 is incident by itself.

The embodiment of FIG. 29 is another example of how a beam splitter canbe used to make a coincidence device. The behavior plays a role in thevarious devices described above and below. This is the case also withthe early embodiments using the transmitting and reflecting gratings asdescribed above with reference to FIGS. 2–11. That is, referring now toFIG. 30, the zero lobe may be regarded as an output which is indicatedas an output 2110 at port 2. As discussed above, the output 2110 energyincident at port 2 is a fourth that of the incident beam when either ofthe input beams at ports 1 or 5 is incident on a grating 2100 alone.When both are coincident on the grating 2100 simultaneously, the energyin the zero order lobe, indicated as an output 2115 at port 2, is onlyhalf that of the total energy incident. Thus, the energy at the output 2in the coincidence state is four times that in the noncoincidence state.

Referring now to FIG. 31 and recalling the discussion of FIG. 19, it maybe confirmed immediately that the Y-junction exhibits a coincidencebehavior, albeit less markedly in terms of intensity. That is, in eithernoncoincidence state, the output is half that of the coincidence state.The energy loss in all states is about 50%. No further explanation ofFIG. 19 is given since the concepts were discussed with reference toFIG. 19.

The same “power combiner” behavior as exhibited by the Y-junction ofFIGS. 19 and 31 is exhibited by another device shown in FIG. 32. A pairof mirrors 220 directs either of two incident beams 2230 and 2245 towardan optical fiber receiver 2220 via a lens 2210. An output beam 2225/2240is proportional to the energy incident on the mirror 2200. In the twononcoincident states, the output is the same intensity as the inputmultiplied by a constant of proportionality. When both beams arecoincident, the output is the combined incident power multiplied by thesame constant of proportionality. As in the previous embodiment, theratio of output during the coincidence state to that during thenoncoincidence state is a factor of two.

Another kind of power combiner that may be used to produce the sameeffect is a reflecting/transmitting grating with very high pitchrelative to the wavelength of light incident thereon. No diffraction,and therefore no interference fringes, are produced because thewavelength of light is substantially greater than the grating spacing.However, inspection of FIG. 33 highlights the similar behavior to thatof a metallic beam splitter with the phase rotation of an incident beam2310 occurring for a reflected beam 2305 and no phase rotation occurringfor a transmitted beam 2300. However, the attenuation of the metallicbeam splitter in noncoincidence states is not present intransmitting/reflecting grating 2315, and thus it functions more as a“power combiner” and not as a coincidence device as does metallic beamsplitter does. In other respects, the behavior of such a grating issubstantially identical to that of a metallic beam splitter for purposesof the coincidence behavior and a discussion of the details is thereforenot provided again.

Referring now to FIG. 34, a coincidence gate that produces zero outputin noncoincidence states and a nonzero output in the coincidence statehas a two part first input signal provided by either the control or datasignal (again, using the illustrative terminology of “control” and“data” employed for purposes of discussing the embodiments) indicated2345 and 2350. For example, the signals that arrive simultaneously toports 1 and 6 are provided by either the control or data signal andsimilarly, the signals that arrive simultaneously to ports 2 and 5 areprovided by either the data or control signal, respectively. These havenon-identical phases which may be derived by any suitable means such asa phase shifter or by suitable delay relationships in input circuitry(not shown here, but exemplified in other embodiments discussed aboveand below as should be clear in the detailed description of theembodiments). The first part 2345 of the input signal is partlyreflected by the beam splitter 2340 and partly transmitted resulting inbeams 2355 and 2347. Although shown, the relative phases of thesesignals has no relevance, but the phase of signal 2347 must be oppositeone produced by the other part 2350 of the input signal via the circuitincluding Y-junction 2365 and phase shifter 2360. That is, the result ofthe combination of the signals at ports 8 and 9 by a final Y-junction2370 should be zero.

Referring now to FIG. 35, an the alternative noncoincidence state, theembodiment of FIG. 34 receives the other of the data or control signalsin two parts 2351 and 2346. These two parts may have identical phaseswhich may be derived by any suitable means such as a phase shifter or bysuitable delay relationships in input circuitry (not shown here, butexemplified in other embodiments discussed above and below as should beclear in the detailed description of the embodiments).

Note that the phase relationships between the two parts (here and inFIG. 34) is arbitrary so long as suitable design is provided in otherparts of the circuit such that the correct interference interactionoccurs. But the relative phases of input signal 2346 and 2351 isimportant to insure that the beam splitter's output to port 4 in thecoincidence state is much greater in magnitude than that produced by thepower combiner 2365 as discussed with regard to FIG. 36, below, whichshows the coincidence state.

Returning to the discussion of the noncoincidence state of FIG. 35, thefirst part 2346 of the input signal is partly reflected by the beamsplitter 2340 and partly transmitted resulting in beams 2356 and 2348.Again, the structure must insure that the phase of signal 2348 isopposite that produced by the other part 2351 of the input signal viathe circuit including Y-junction 2365 and phase shifter 2360. That is,the result of the combination of the signals at ports 8 and 9 by a finalY-junction 2370 should be zero.

Referring now to FIG. 36, when respective parts 2345 and 2346 of boththe data and control signals are incident on the beam splitter 2340, allthe energy of the two signals emerges at port 4 as a signal 2375. Thephase of this signal 2375 is the same as that in each of thenoncoincidence states, but it is four times the magnitude, that is, 2I.The Y-junction combines the other parts 2350 and 2351 of the data andcontrol signals, but the resulting intensity is only twice that in thenoncoincidence states of FIGS. 34 and 35. Thus, when combined with thesignal in the Y-junction 2370, a non-zero output 2380 at port 10 isobtained.

In terms of the relative intensity, the behaviors of the device of FIGS.34–36 is essentially the same as that described with respect to FIGS. 20and 21. To apply signals to the various inputs of the device of FIGS.34–36, the same input circuitry 1993, 1994, 1995, and 1996 (shown inFIGS. 22–27) as added to corresponding parts (i.e., applied at ports 1,2, 5, and 6) to the device of FIGS. 20 and 21 may be used. That is, theinput circuit portions 1993, 1994, 1995, and 1996 may be used as well asvariations thereof discussed above and the wide variety others that maybe envisioned based on the principles presented herein.

Note that although the above embodiment of FIGS. 34–36 included adielectric beam splitter 2340, it is clear that other types of devicesmay be used to achieve the same effect. For example, a metallic beamsplitter could be substituted, with appropriate circuiting to providethe required phase relationships as illustrated by FIG. 29.

Referring now to FIG. 37, the present embodiment is similar to that ofFIGS. 34–36 except that a different power combiner 2420 of the typediscussed relative to FIG. 32 is used and the input signal portionsapplied to it indicated (schematically) to have an input phase that is πahead of that provided in the embodiments of FIGS. 34–36. That is, aportion 2351′ of one of the data and control signals has an initialphase of π. Again, as should be clear, the input phases are arbitrary solong as the circuitry design provides appropriate interaction withincomponents where the signals interfere.

The power combiner 2420 includes a mirror pair 2410, a lens 2405, and areceiving port 2425 of an optic fiber. The signal 2351′ is attenuated bythe insertion process, but is proportional to the initial signal and isshown at port 7 with an intensity of I/2 and a phase that is π ahead (orbehind) that at port 4, as symbolized by the multiplier −J. The port 4signal is as in the previous embodiments. An attenuator/amplifier 2415is included to indicate that the circuitry needs to ensure the output ofthe Y-junction 2370 is zero.

Referring now to FIG. 38, the complementary one of control and datasignals is applied in respective portions 2345 and 2350′ to the ports 2and 6, respectively with the same result as in FIG. 37 with a zerooutput at port 10 of the Y-junction 2370.

Referring now to FIG. 39, as in the coincidence state illustrated inFIG. 36 and the attending discussion, when respective parts 2345, 2346of both the data and control signals are incident on the beam splitter2340, all the energy of the two signals emerges at port 4 as the signal2375. Here again, the phase of this signal 2375 is the same as that ineach of the noncoincidence states, but it is four times the magnitude,that is, 2I. The Y-junction combines the other parts 2350′ and 2351′ ofthe data and control signals, but, as with the embodiment of FIGS.34–36, the resulting intensity is only twice that in the noncoincidencestates of FIGS. 37 and 38. Thus, when combined with the signal in theY-junction 2370, a non-zero output 2381 at port 10 is obtained. Again,as before and although it hardly bears repeating, the phase of the finaloutput 2381 is arbitrary and will depend on the precise details of thedesign and may even depend on the environmental conditions.

Referring now to FIG. 40, yet another kind of energy combiner may beused with the circuit portions of the embodiment of FIGS. 34–36 commonto that of FIGS. 37–39. The combiner in this embodiment is a zero ordergrating 2460 as discussed above with regard to FIG. 33. Here, as in FIG.35, the first and second portions 2351 and 2346 either of the datasignal or the control signal are applied simultaneously to thepower-combiner zero order grating 2460 at the equivalent port 5 and tothe beam splitter 2340 at port 1. The results are identical to thoseshown in FIG. 35 and discussed with respect thereto. That is, theemerging signal applied at port 7 is phase-shifted to oppose the signalapplied at port 8 with the result that the port 8 and 9 signalsinterfere in the Y-junction 2370 and output essentially no signal atport 10. The common features are not discussed again, since they shouldbe clear from the discussion of FIGS. 34–39.

Referring now to FIG. 41, the complementary signals either from the datasignal or from the control signal are applied simultaneously at ports 2and 6 with a similar result that is essentially as described withrespect to FIG. 34. Finally, referring to FIG. 42, in a coincidencestate, a non-zero output 2382 is obtained for reasons that should beclear from the previous discussion of previous embodiments. In theembodiment of FIGS. 40–42, the zero order grating 2460 acts as an energycombiner just as the Y-junction 2365 and the power combiner 2420. Thecommon elements of FIGS. 40–42 need not be described again since theyfunction essentially as described in previous embodiments to produce asimilar result. As with the embodiment of FIGS. 34–36 to apply signalsto the various inputs of the device of FIGS. 37–39 and that of FIGS.40–42, the same input circuitry 1993, 1994, 1995, and 1996 (shown inFIGS. 22–27) as added to corresponding parts (i.e., applied at ports 1,2, 5, and 6) to the device of FIGS. 20 and 21 may be used. That is, theinput circuit portions 1993, 1994, 1995, and 1996 may be used as well asvariations thereof discussed above and the wide variety others that maybe envisioned based on the principles presented herein.

Principles of some of the foregoing embodiments may be extended to otherembodiments easily in view of the following abstraction. In many of theforegoing embodiments, each of two signals is combined, in a firstprocess, to produce a first output of a first power level and in asecond process to produce a second output of a second power level. Thefirst and second processes are such that the same signals individuallyare combined in the first and second processes to produce, respectively,a third output at third power level and a fourth output at the samethird power level. The third and fourth outputs are caused to interferein a third process such that they cancel. The first and second outputsare also caused, by the same third process to cancel, but the thirdprocess of cancellation is such that, because the first output is at ahigher power level than the second, residual energy remains after thecancellation process. Thus, when both signals are processed to producefirst and second outputs, a non-zero output is obtained. When eithersignal is processed alone, no output is obtained.

Referring to FIG. 43, to illustrate the above abstraction, the firstprocess is represented here as a black box labeled“augmentation/cancellation process 1500.” The latter has one or moreoutputs. The augmentation/cancellation process 1500 is such that the oneor more outputs have a combined power that is a higher proportion of thetotal input power when both signals 1 and 2 are incident than wheneither signal 1 or 2 is incident alone. Examples of these are thedirectional coupler, dielectric or metallic beam splitter, and aspectsof the transmission/reflecting grating and spatial interference device800.

Referring to FIG. 44, the second process is represented here as a blackbox labeled “power combiner 1510.” The latter has one or more outputs.The power combiner process 1510 is such that the one or more outputshave a combined power that is proportional to the total input power whenboth signals 1 and 2 are incident as well as when either signal 1 or 2is incident alone. Examples of these are the reverse Y-junction, thezero order grating, and the power combiner of FIG. 32. Referring now toFIG. 45, a power combiner, which may be identical to the power combiner1510, combines outputs 1 and 2 such that the output 3 is proportional tothe combined power of the inputs if the two outputs interfereconstructively and which is zero if the two signals have the sameintensity and interfere destructively. As a result of the nonlinearityof the signal levels at output 1 of the augmentation/cancellationprocess 1500 as a function of the signal arrangement in inputs 1 and 2,the power level of output 3 can, by judicious design of the processes1500 and 1510 and/or processing of the outputs 1 and 2, be made toresult in a zero output 3 when input signals 1 and 2 are incident aloneand produce at output 1 a signal to be equal to output 2 but of acharacter that when combined in power combiner 1520 they cancel (e.g.,have an opposite phase). A nonzero output 3 results when input signals 1and 2 are incident simultaneously and produce an output 1 that isgreater than output 2 (coincident state).

While the above description contains many details, these should not beconsidered as limitations on the scope of the invention, but as examplesof the presently preferred embodiments thereof. Many other ramificationsand variations are possible within the teachings to the invention.

For example the all-optical switches, modulators, encoding and decodingsystems, interleaving and multiplexing systems, and demultiplexingsystems have been described for use in communication networks. Howeverthey can be used in other optical systems as well, such as systems usedfor optical computing. They also can be used as optical components,devices, and systems in Ethernet systems. Although the invention beendescribed using the examples of DTDM and self-triggered CDM it can beused for producing very narrow pulses to perform standard techniques,such as TDM, ATM and packets routing.

Although the some systems have been described as modulators they alsocan be operated as switches. While some all-optical encoding andmultiplexing systems have been described using sub-units operating asmodulators, the situation can be reversed, i.e., the operation of thesesame sub-units can be change to serve as switches in decoding anddemultiplexing systems. Though some switches and modulators have beendescribed with one output they can include multiple outputs. While themodulators and the switches have been described as containing gratingsor phase arrays, they can also include another interference devices thatare capable of changing their pitch according to the illuminationconditions. Although the gratings and the phase arrays have beendescribed as having one ore three interference orders, they are notlimited to these numbers of interference orders. While some of theswitches and the modulators are illustrated without optical amplifiersthey can be integrated with optical amplifiers, such as a Europium DopedOptical Fiber Amplifier (EDOFA).

Thus the scope of the invention should be determined by the appendedclaims and their legal equivalents, and not by the examples given.

It will be evident to those skilled in the art that the invention is notlimited to the details of the foregoing illustrative embodiments, andthat the present invention may be embodied in other specific formswithout departing from the spirit or essential attributes thereof. Thepresent embodiments are therefore to be considered in all respects asillustrative and not restrictive, the scope of the invention beingindicated by the appended claims rather than by the foregoingdescription, and all changes which come within the meaning and range ofequivalency of the claims are therefore intended to be embraced therein.

1. A method of producing narrow optical pulses by optical chopping, themethod comprising: receiving first and second optical pulses havingfirst and second widths, respectively, and substantially the same pulserate, wherein the second optical pulse has a delay relative to the firstoptical pulse; and selectively interfering said first and second opticalpulses to produce a third optical pulse having a third width narrowerthan both said first and second widths, and having substantially thesame pulse rate as said first and second optical pulses, wherein asegment of the first optical pulse overlaps in time with the secondoptical pulse and wherein said third width is substantially equal to awidth of said segment.
 2. The method of claim 1, wherein said thirdwidth of said third optical pulse corresponds to said delay between thefirst and second optical pulses.
 3. The method of claim 1, furthercomprising adjusting said delay to produce a desired value for saidthird width.